GIFT  ©F 
Prol.   E.  JVwickson 


B10L03Y 


Edward  J.  '. 


MEE 


BY 
MAXWELL  T.  MASTERS,  M.D.,  F.R.S. 


NEW   YORK: 

ORANGE    JUDD    COMPANY, 

751    BROADWAY. 

1885. 


Q  \<  HI 


BIOLOGY 

LIBRARY 

G 


0     J  t 


MAIM  UiMtARY.*t«ft*COi.TUttC 


Entered,  according  to  Act  of  Congress,  in  the  year  1884,  by  the 
ORANGE   JUDU    COMPANY, 

lu  the  Office  of  the  Librarian  oi  Congress,  at  Washington. 


PREFACE 


Rightly  to  understand  what  work  is  done  by  living 
plants,  and  how  it  is  effected,  not  only  requires  a  student 
to  be  a  botanist  in  the  ordinary  sense  of  the  word,  but 
necessitates  that  he  should  also  •  have  a  comprehensive 
knowledge  of  physics  and  of  chemistry. 

In  few  individuals  can  such  an  extensive  knowledge 
now-a-days  be  expected.  The  practical  cultivator  espe- 
cially, harrassed  by  the  daily  cares  of  his  occupation,  is 
not  able  to  master  the  endless  details  of  these  sciences  ; 
and  yet  experience  shows  the  increasing  necessity  for 
furnishing  him  with  new  tools  and  new  weapons  to 
enable  him  to  utilize  the  resources  of  Nature,  and  to 
contend  against  adverse  circumstances.  Such  tools,  such 
weapons  are  furnished  by  the  armory  of  science.  It  is 
the  object  of  this  Handbook  to  point  out  the  nature  of 
these  resources,  and  suggest  the  methods  of  utilizing 
them.  Something  will  be  gained  if  only  a  right  appre- 
ciation of  what  cannot  be  done  is  obtained,  as  thereby 
labor  on  a  sterile  soil  will  be  avoided,  to  be  applied  with 
more  reasonable  hope  of  success  elsewhere. 

In  the  following  pages  an  attempt  has,  therefore,  been 
made  to  supply  a  sketch,  necessarily  in  faintest  outline, 
of  the  physiology  or  life-history  of  plants  ;  of  the  way  in 
which  they  are  affected  by  the  circumstances  under  which 
they  exist,  and  of  the  manner  in  which  they  in  their  turn 
react  upon  other  living  beings  and  upon  natural  forces* 
Of  necessity,  there  has  been  a  little  overlapping  in  the 
case  of  some  of  the  subjects  treated  of  in  the  companion 
volume,  "  The  Chemistry  of  the  Farm,"  by  Mr.  Waring- 
ton ;  but  as  the  matters  are  looked  at  from  a  different 

(in) 

"^  ~    *   * 

6 


IV  PKEFAC& 

stand-point,  and  as  no  pretence  is  here  made  to  impart 
special  chemical  knowledge,  it  is  hoped  that  Mr.  Waring- 
ton  and  the  reader  also  will  forgive  any  slight  incursions 
into  a  territory  which  the  writer  has  no  claim  to  enter 
except  upon  sufferance. 

Structural  botany,  whether  dealing  with  the  outer  con- 
formation or  the  internal  organization  of  plants,  is  only 
incidentally  treated  of  in  these  pages ;  the  classification 
of  plants  is  also  passed  over  without  notice,  as  not  coming 
within  the  scope  of  this  Handbook. 

Detailed  text-books  of  Botany,  or  of  Vegetable  Phy- 
siology, expressly  adapted  to  the  requirements  of  agri- 
culturists do  not  exist,  but  there  are  many  works  from 
which  a  comprehensive  general  idea  of  the  present  state 
of  knowledge  of  these  subjects  may  be  obtained. 

In  the  compilation  of  the  following  pages  the  writer 
has  availed  himself  of  Van  Tieghem's  "  Traite  de  Botani- 
que,"  the  French  translation  of  Sachs'  "  Physiologie 
Vegetale"  by  Micheli,  and  Deherain's  "  Cours  de  Chimie 
Agricole,"  etc.  The  works  and  memoirs  of  Darwin  have, 
of  course,  been  laid  under  contribution,  as  well  as  nu- 
merous scattered  papers  by  various  authors.  More  es- 
pecially the  writer  has  to  acknowledge  his  obligations  to 
the  voluminous  records  of  the  noble  series  of  cultural 
experiments  carried  out  at  Eothamsted  for  so  many  years 
by  Sir  J.  B.  Lawes  and  Dr.  Gilbert.  The  "  Memorandum 
Sheet "  published  by  these  experimenters  supplies  annu- 
ally a  condensed  summary  of  the  results  of  their  experi- 
ments, and  is  a  document  that  should  be  carefully 
studied  with  due  reference  to  its  professed  object,  by  all 
who  have  the  advancement  of  agricultural  knowledge  at 
heart.  M.  T.  M. 


CONTENTS. 


CHAP.  PAGE, 

I.— PLANT  NUTRITION  :  THE  WORK  AND  THE  MATE- 
RIALS                              7-21 

II.— NUTRITION.— THE  MACHINERY 22-44 

III. — GROWTH 44-  55 

IV. — SENSITIVENESS 56-  70 

V.— DEVELOPMENT 71-  81 

VI. — MULTIPLICATION 81-  89 

VII.— THE  BATTLE  OF  LIFE 89-109 

VIII.— PRACTICAL  INFERENCES 109-124 

IX.— DECAY  AND  DEATH  ._  124-130 


INDEX _  —  ---._--...„- _____     131-132 


PLANT  LIFE  ON  THE  FARM, 


CHAPTEE  I. 
PLANT-NUTRITION  :  THE  WORK  AND  THE  MATERIALS. 

Introductory  remarks. — What  plants  do  and  how  they  do  it. — Receipts. 
—  Expenditure.  —  Accumulation.  — Transformation.  —  How  plants 
feed. — Influence  of  temperature. — Water  and  the  machinery  by 
which  it  is  supplied  and  distributed. — Protoplasm. — Cells  and  their 
contents. — Ingress  and  movements  of  water. — The  first  stage  of 
nutrition. — Diffusion. — Osmosis  and  the  requisite  conditions  for  it. 
— Saturation. — Varying  degrees  of,  according  to  the  nature  of  the 
liquid. — Amount  absorbed. — Supply  and  demand. — Differences  of 
composition  of  plants  grown  in  the  same  soil,  how  explained. — 
Continuous  change. — Nutritive  value  of  water. — Nitrates ;  agency 
of  Bacteria.  —  Potash.  — Sulphur.  — Phosphorus. — Iron. —  Lime. — 
Principles  of  manuring. — Power  of  selection. 

He  who  can  make  two  blades  of  grass  grow  where  only 
one  grew  before  is  universally  looked  on  as  a  benefactor 
to  his  kind.  No  one  will  dispute  his  title  to  our  grati- 
tude ;  but  at  the  same  time  it  must  not  be  overlooked 
that  the  claims  of  him  who  can  make  one  grow  where 
none  at  all  existed  before,  are  even  greater,  because  the 
difficulties  to  be  overcome  are  more  formidable,  for  where 
one  exists  already  it  is  relatively  easy  to  bring  about  its 
increase. 

In  any  case,  it  is  clear  that,  before  either  problem  can 
be  satisfactorily  solved,  as  full  a  knowledge  as  possible  of 
all  the  conditions  requisite  for  the  process  must  be  in 


LIFE   OK  THE   FAKM. 


some  way  or  another  obtained.  Success  in  a  practical 
pursuit  like  agriculture,  depends  largely  on  the  extent  of 
our  knowledge,  and  still  more  upon  our  power  of  apply- 
ing it  under  various  circumstances.  In  the  following 
notes  an  attempt  will  be  made  to  supply  indications  of 
some  among  the  phenomena  of  the  life  of  plants  of  which 
it  seems  most  desirable  that  the  cultivator  should  take 
heed.  Some  slight  knowledge  of  the  general  conforma- 
tion of  plants  on  the  part  of  the  reader  is  assumed,  but 
explanations  of  the  more  important  points  will  be  given. 
A  living  plant  feeds,  breathes,  grows,  developes,  mul- 
tiplies, decays,  and  ultimately  dies.  In  so  doing  it  re- 
ceives, it  spends,  it  accumulates,  it  changes.  Some  of 
these  processes  are  always  in  operation,  very  generally 
more  than  one  is  going  on  at  the  same  time,  and  the 
action  of  one  is  modified  by  and  controlled  by  that  of 
another.  Some  circumstances  and  conditions  favor  these 
operations,  others  hinder  them.  The  practical  cultiva- 
tor has  his  concern  in  all  these  matters,  so  that  it  is  of 
no  slight  moment  to  him  to  realize  what  is  the  work 
which  a  plant  does,  and  how  it  does  it. 

How  Plants  Feed.—  The  nutritive  process  has  to  be 
entered  on  the  creditor  side  as  a  receipt.  The  plant  will 
indeed  feed  upon  itself  for  a  time,  or  rather  it  will  feed 
upon  what  its  predecessor  left  it  as  an  inheritance  for  this 
very  purpose,  or  upon  the  stores  accumulated  in  the  plant 
itself  during  the  preceding  season  ;  thus,  when  a  seed,  or 
rather  the  young  plant  within  the  seed,  begins  to  grow,  it 
is  at  first  unable  to  forage  for  itself,  but  it  depends  for 
its  sustenance  on  the  materials  laid  up  for  its  use  during 
the  preceding  season  by  the  parent  plant.  So  the  bud  of 
a  tree  awakening  into  life,  and  beginning  its  career  as  a 
shoot  which  is  to  bear  leaves  and  flowers,  derives  its  first 
meals  from  the  reserves  accumulated  the  autumn  previ- 
ously in  the  parent  branch.  Very  generally  a  little  water, 


PLANT  NUTRITIOK.  9 

supplied  from  without,  is  required  before  the  plant  can 
avail  itself  of  these  stored-up  provisions,  but  this  is  not 
always  indispensable.  Potatoes  begin  to  sprout  in  their 
cellars  or  pits,  as  growers  know  to  their  cost,  before  they 
can  have  obtained  a  drop  of  water  from  without.  In 
this  latter  case  there  is  water  enough  already  in  the  tu- 
ber to  allow  of  food  being  utilized. 

Effect  of  Temperature, — A  certain  degree  of  useful 
heat  is,  of  course,  quite  indispensable.  Practically,  no 
plant  will  feed  when  its  temperature  is  reduced  as  low  as 
the  freezing  point,  and  in  most  cases  the  heat  requires  to 
be  considerably  greater.  Each  kind  of  plant,  each  indi- 
vidual -plant,  and  indeed  each  part  of  a  plant,  feeds,  and 
performs  each  item  of  its  life-work,  best  at  a  certain  tem- 
perature, and  ceases  to  work  at  all  when  the  temperature 
falls  below  or  rises  above  a  certain  point.  The  particu- 
lar degree,  whether  most  or  least  favorable,  varies  accord- 
ing to  the  plant,  its  age,  stage  of  growth  and  various  ex- 
ternal circumstances,  which  we  need  only  mention,  as 
their  effects  will  be  readily  understood  without  the  ne- 
cessity of  explanation. 

It  is  clear  then  that  a  suitable  temperature  and  access 
of  water,  either  liquid  or  in  the  form  of  vapor,  are  the 
first  essentials  in  the  feeding  process  in  plants.  Practi- 
cally, and  from  force  of  circumstances,  the  gardener  has 
more  control  over  both  temperature  and  the  supply  of 
water  than  the  farmer  ;  nevertheless  by  drainage,  by 
choice  of  aspect,  site,  by  shelter,  and  other  means,  even 
the  farmer  has  some  power  to  regulate  the  temperature 
and  the  amount  or  influence  of  water  to  which  his  crops 
are  subjected. 

Water, — Leaving,  however,  on  one  side,  the  temper- 
ature, we  have  to  consider  the  water  which  is  so  essential, 
not  only  in  the  feeding  processes  with  which  we  are  now 
concerned,  but  with  every  other  action  of  plant  life. 


10  PLANT  LIFE  ON  THE   FAKM. 

Fortunately  there  is,  in  general,  no  lack  of  it ;  the  earth 
and  the  air  contain  their  shares  of  this  elementary  com- 
pound in  varying  proportions  and  varying  modifications 
as  liquid  or  gaseous.  Besides,  the  plant  itself  has  so 
much  of  it  that  even  at  the  driest  condition  compatible 
with  life,  it  still  constitutes  a  very  large  proportion  of  the 
entire  weight.  Now,  it  is  as  a  rule  when  the  plant,  the 
seedling,  or  the  bud  is  at  its  driest  that  growth  begins, 
the  necessity  for  food  first  manifests  itself,  and  the  demand 
for  a  further  supply  of  water  becomes  imperative.  How 
is  the  demand  supplied  ?  We  have  seen  that  there  is  no 
lack  of  that  fluid.  How  is  it  to  get  into  the  plant  ? 
The  answer  to  this  question  brings  us  at  once  to  the  con- 
sideration of  the  raw  material  and  of  the  fabric  of  plants 
by  whose  agency  alone  it  is  that  the  water  gains  entrance 
to  the  plant. 

Ingress  and  Movements  of  Water ;  Diffusion,  Osmo- 
sis.— Our  first  inquiry,  then,  must  be  to  ascertain  how 
the  water,  whose  presence  in  sufficient  quantity  we  have 
assumed,  gets  from  without  through  the  cell-membrane 
into  the  protoplasm — how,  in  fact,  the  first  stage  in  inde- 
pendent nutrition  is  accomplished.  When  one  liquid, 
say  spirit,  is  poured  into  another,  say  water,  the  two 
gradually  mix.  If  we  suppose  these  liquids  to  consist  of 
a  number  of  molecules,*  then,  mixture  may  be  taken  to 


*It  may  be  well,  once  for  all,  to  explain  the  sense  in  which  the  term 
"molecule"  is  here  used.  It  is  now  generally  assumed  by  physicists 
that  every  substance  in  nature  is  made  up  of  excessively  minute  parti- 
cles called  atoms,  which  are  indestructible.  An  atom  cannot  exist  by 
itself,  but  in  association  with  others.  Such  a  group  of  atoms  is  called  a 
"  molecule."  A  molecule,  therefore,  is  the  smallest  group  of  atoms 
capable  of  existing  separately  and  independently.  These  molecules  may 
be  of  different  sizes  in  different  cases,  and  they  are  believed  to  be  so 
arranged  as  just  not  to  touch,  but  to  leave  spaces  between  them  ; 
smaller  in  the  case  of  a  hard  solid,  wider  in  that  of  a  liquid,  still  wider 
in  that  of  a  gas.  The  extent,  moreover,  of  these  interspaces  may  be 
increased  or  diminished  by  varying  degrees  of  heat, 


PLANT   NUTRITION.  11 

be  the  result  of  the  displacement  say  of  one  molecule  of 
water  by  one  molecule  of  spirit,  and  so,  throughout  the 
whole  quantity  of  liquid,  there  is  displacement  and  re- 
placement until  at  length  equilibrium  is  restored  and  a 
thorough  diffusion  results.  This  power  of  diffusion  does 
not  always  exist.  The  molecules  of  water  and  of  oil  will 
not  mix  or  diffuse  freely  through  each  other.  "Water 
containing  carbonic  acid  gas  will  not  mix,  in  this  sense 
of  the  term,  with  water  containing  acetate  of  lead  ;  and 
when  the  attempt  is  made,  chemical  change  is  set  up, 
the  heretofore  clear  solutions — that  containing  the  gas 
and  that  containing  the  lead  -become  when  combined 
opaque  and  milky,  owing  to  a  chemical  change,  resulting 
in  the  formation  of  a  white  insoluble  lead  carbonate. 

It  may  be  a  truism  to  say,  that  for  the  process  of  dif- 
fusion the  liquids  must  be  diffusible,  but  the  fact  must 
be  carefully  borne  in  mind  in  all  questions  relating  to  the 
feeding  of  plants.  In  the  case  of  plants,  the  phenomenon 
of  diffusion,  or  the  gradual  admixture  of  two  liquids  of 
different  natures,  is  complicated  by  the  presence  of  a 
membrane  in  the  shape  of  the  cell-wall.  The  water  from 
the  outside  has  to  pass  through  the  membrane  to  reach 
the  protoplasm  on  the  other  side.  Speaking  broadly, 
there  are  no  holes  in  the  membrane  through  which  the 
water  can  pass.  Ingress  is  secured  by  that  process  of  dif- 
fusion to  which  reference  has  just  been  made,  and  by 
virtue  of  which  the  molecules  of  the  membrane  and  the 
molecules  of  the  water  shift  and  change  places  ;  the 
space  that  was  occupied  by  a  molecule  of  membrane  is 
now  occupied  by  a  molecule  of  water,  and  vice  versa. 
The  access,  therefore,  of  water  into  the  interior  of  a 
closed  cell  is  the  result  of  the  process  of  diffusion. 
Where  two  liquids  mix  without  any  intervening  mem- 
brane, the  mixture  is  called  diffusion  simply  ;  where 
there  is  an  intervening  membrane,  the  diffusion  process 


12  PLANT  LIFE   OiT  THE   FAEM. 

Protoplasm — Cells, — The  raw  material  (the  term  is  not 
quite  accurate,  but  for  illustration  sake  it  may  pass)  is 
that  very  marvellous  substance  now  called  "  protoplasm." 
We  must  leave  it  to  chemists  and  microscopists  to  ex- 
plain its  composition  and  indicate  its  appearance.  Suffice 
it  here  to  call  it,  as  Huxley  did,  "the  physical  basis  of 
life. "  Without  it,  or  when  it  is  dead,  the  plant  is  dead 
too ;  with  it  the  plant  lives,  without  it  it  dies.  It  is  a 
viscid,  colorless,  jelly-like  substance,  endowed  with  all 
those  varied  properties  which  constitute  in.  the  aggregate 
all  that  we  can  tangibly  realize  of  the  manifestations  of 
life. 

With  few  exceptions,  which  it  is  not  necessary  here  to 
particularize,  the  protoplasm  does  not  exist  in  one  un- 
broken mass,  but  is  contained  in  little  membranous  bags 
called  "  cells."  These  cells  are  of  various  shapes  and 
sizes,  and  may  undergo  various  modifications  during  the 
growth  of  the  plant.  They  are  large  enough  to  be  seen 
by  the  naked  eye  in  the  pulp  of  an  orange,  but  usually 
they  require  the  aid  of  the  microscope  to  discern  them. 
They  are  lengthened  into  tubes  placed  end  to  end  to  form 
conduits,  or  thickened  into  fibres.  The  cells,  then,  vari- 
ously combined  and  modified,  constitute  what  we  have 
termed  the  fabric  of  the  plant.  Each  living  cell  consists 
essentially  of  a  certain  proportion  of  protoplasm  contained 
within  a  membranous  bag  or  bladder,  called  technically 
the  "cell-wall."  There  may  be,  and  generally  are,  other 
things  besides  the  protoplasm  within  the  cell-wall,  such, 
for  instance,  as  a  small  ovoid  body  known  as  the  "  nu- 
cleus," and  green  coloring  matter  or  "chlorophyll ;"  but 
these  other  things,  important  as  they  are,  we  may  leave 
out  of  consideration  for  the  present. 

Every  plant  and  every  part  of  every  plant  is  made  up 
of  cells  such  as  have  been  mentioned.  As  a  cell  a  plant 
begins  its  independent  life ;  with  and  by  cells  it  lives, 
grows,  multiplies ;  by  their  decay  it  dies.  It  is,  as  has 


PLANT   NUTRITION.  13 

been  said,  the  protoplasm,  which  is  the  essential  agent 
in  all  these  processes  ;  but,  subject  to  a  few  exceptions, 
which  need  not  now  be  specified,  this  protoplasm  is 
always  shut  up  within  a  cell-wall.  Nor  is  it  absolutely 
necessary  that  there  should  be  more  than  one  cell.  Most 
plants  with  which  the  cultivator  has  to  do  consist  of  ag- 
gregations of  such,  but  there  are  myriads  of  other  plants 
which  consist  of  but  one  cell ;  in  such  a  case  the  cell  is 
the  plant,  the  plant  is  the  cell.  Now  this  is  important, 
because  it  shows  us  that  all  the  processes  of  life  can  be, 
and  often  are,  carried  on  in  one  cell  only,  that  is,  by  one 
fragment  of  protoplasm.  Where  the  fabric  becomes 
more  complex,  one  cell  is  more  or  less  dependent  on 
another,  but  still  there  is  always  a  measure  of  indepen- 
dence left  to  each  individual  cell.  Were  it  not  so,  the 
scythe  of  the  mower  or  the  grazing  of  the  sheep,  by  de- 
stroying a  portion,  would  kill  the  entire  plant. 

It  follows  that  the  life-history  of  a  plant  is,  in  essence, 
the  life-history  of  protoplasm  and  of  its  covering,  the 
cell-wall ;  and  hence  it  is  that  the  microscopist  or  the 
chemist  in  the  laboratory  studying  what  goes  on  in  isolat- 
ed cells,  placed  as  far  as  possible  under  uniform  condi- 
tions, is  really  adopting  the  best  means  of  investigating 
what  takes  place  in  the  entire  plant ;  a  circumstance 
which  the  "practical  man,"  so  called,  compelled  to  work 
in  the  field  under  such  very  different,  more  complex  and 
much  less  definite  conditions,  finds  it  difficult  to  realize. 

Conditions  of  Diffusion,— Diffusion,  it  will  readily  be 
understood  from  what  has  just  been  said,  is  not  equal  or 
alike  in  all  cases  ;  it  depends  upon  the  extent  to  which 
the  two  liquids  are  diffusible,  upon  their  different  densi- 
ties, upon  temperature,  and  a  variety  of  other  conditions. 
So,  in  the  case  of  osmosis,  we  have  not  only  the  nature 
of  the  two  fluids  to  consider,  but  their  relation  to  the 
membrane  that  separates  them.  The  membrane  may  be 


14  PLANT  LIFE  ON  THE   FARM. 

much  more  permeable  to  one  of  the  two  fluids  than  to 
the  other.  Thus,  in  the  case  of  a  living  cell,  the  mem- 
brane or  wall  is  much  more  permeable  to  water  than  it  is 
to  protoplasm ;  and  so  it  happens  that,  while  water 
readily  penetrates  the  membrane  and  diffuses  itself  in  the 
protoplasm,  protoplasm  does  not  nearly  so  readily  per- 
meate the  membrane  as  the  water.  Ingress  of  water  is 
easy  and  of  constant  occurrence,  egress  of  protoplasm  is 
rare  and  exceptional. 

Pure  water  or  weak  saline  solutions,  such  as  are  gener- 
ated in  the  soil  under  certain  circumstances,  pass  readily 
through  membrane — that  is,  the  molecules  of  the  one 
shift  and  change  places  with  those  of  'the  other — while 
those  of  gummy  or  albuminoid  substances  like  proto- 
plasm do  not.  After  a  time,  if  there  is  no  outlet  for  the 
water  absorbed,  or  if  it  is  not  utilized  within  the  plant  in 
some  way,  absorption  and  diffusion  cease,  the  cell  becomes 
saturated  with  water,  and  until  something  happens  to 
disarrange  the  balance,  no  more  is  absorbed.  But,  even 
in  the  case  where  the  cell  is  saturated  with  water,  it  may 
still  take  up  other  liquids,  because  the  diffusive  power 
of  those  other  liquids,  in  relation  to  the  cell-wall  and  to 
the  protoplasm,  is  different  from  that  of  water,  and  this 
absorption  must  go  on  in  its  way  till  saturation  point  is 
reached  for  each  one  of  them,  just  as  in  the  case  of  water. 
On  the  other  hand,  it  may  happen  that  the  plant  may  be 
saturated  with  other  substances,  and  incapable  of  taking 
up  more  of  them,  while  at  the  same  time  pure  water  may 
be  freely  taken  up. 

Quantity  absorbed. — Just  so  much  and  no  more  of 
each  particular  substance  is  absorbed,  the  exact  quantity 
of  each  being  regulated  in  all  cases  by  the  condition  and 
requirements  of  the  cells,  their  membranous  walls,  and 
their  contents.  Thus  it  happens  that  some  particular 
substances  may  be  found  by  the  chemist  to  exist  in  large 


PLANT  NUTKITIOST.  15 

relative  proportions  in  the  plant,  while  the  quantity  in 
any  given  sample  of  the  soil  from  which  it  must  be  de- 
rived, is  sometimes  so  small  as  to  elude  detection.  The 
plant  in  this  case,  or  some  part  of  it,  is  so  greedy,  if  we 
may  so  say,  for  this  particular  substance,  that  it  absorbs 
all  within  its  reach,  and  stores  it 'up  in  its  tissues  or  uses 
it  some  way,  the  demand  ensuring  supply.  On  the 
other  hand,  the  soil  may  contain  a  large  quantity  of 
some  particular  ingredient  which  is  incapable  of  being 
absorbed,  or  which  the  plant  does  not  or  cannot  make 
use  of,  and,  in  consequence,  none  is  found  within  the 
plant.  The  supply  is  present,  but  there  is  no  demand. 

The  different  physical  requirements  of  the  plant  sup- 
ply also  the  explanation  of  the  fact  that  different  plants, 
grown  in  the  same  soil,  supplied  with  the  same  food,  yet 
vary  so  greatly  in  chemical  composition.  Thus,  when 
wheat  and  clover  are  grown  together,  and  afterwards 
analyzed,  it  is  found  that  while  lime  is  abundant  in  the 
clover,  it  is  relatively  in  small  quantity  in  the  wheat  ; 
and  silica,  which  is  abundant  in  the  wheat,  is  absent 
from  the  clover.  Poisonous  substances  even  may  be  ab- 
sorbed, if  they  are  of  such  a  nature  as  to  be  capable  of 
absorption ;  and  so  the  plant  may  be  "killed  by  its  own 
action — by  suicide,  as  it  were. 

The  entrance  of  water  into  the  plant  and  the  entrance 
of  those  soluble  materials  which  a  plant  derives  from  the 
soil  are  therefore  illustrations  of  the  process  of  osmosis, 
and  are  subjected  to  all  the  conditions  under  which  os- 
mosis becomes  possible,  or  under  which  it  ceases  to  act. 
The  study  of  these  conditions  is  a  question  for  the  physi- 
cist, and  the  full  explanation  of  them  must  be  sought  in 
works  relating  to  physics.  So  the  investigation  of  the 
substances  which  are  absorbed  with  the  water,  of  the 
food  materials,  and  their  transformations  within  the 
plant,  is  the  work  of  the  chemist,  and  their  history  must 
be  sought  in  chemical  books. 


16  PLAKT   LIFE   OK   THE   FA11M. 

Continuous  Changes  in  Plants,— In  this  place  we  must 
confine  ourselves  to  the  few  passing  references  already 
made,  but  one  thing  we  must  strive  to  impress  forcibly 
on  the  reader,  because,  if  the  notion  is  well  grasped,  it 
will  enable  him  to  understand  plant  life  so  much  more 
vividly.  We  allude  to'  the  continual  changes  that  are 
going  on  throughout  the  whole  living  fabric  of  the  plant 
while  in  its  active  condition.  Cell  membrane,  the  pro- 
toplasm, the  entire  mass  of  liquid  and  solid  constituents 
of  which  the  plant  consists,  are,  as  we  have  seen,  made 
up  of  molecules,  each,  as  it  were,  with  a  life  of  its  own, 
undergoing  continual  changes  according  to  different  cir- 
cumstances, acting  and  reacting  one  upon  another,  so 
long  as  any  active  life  remains.  Active  life,  indeed,  is 
ceaseless  change ;  dormant  life  is  a  condition  of  equi- 
librium, more  often  talked  about  than  realized — in  fact, 
it  is  merely  relative — it  implies  merely  a  lessened  degree 
of  activity.  From  this  physical  point  of  view  the  death 
of  a  cell  is  only  a  change,  a  rearrangement  of  particles, 
never,  however,  to  be  recombined  into  a  new  growing 
cell,  as  happens  in  the  case  of  a  still  living  cell  in  the 
full  tide  of  growth  and  activity. 

Nutritive  Value  of  the  Substances  absorbed  by  Plants, 

— The  importance  of  water  may  be  judged  from  the  fact 
that  while  succulent  vegetables  contain  more  than  ninety 
per  cent  of  water,  timber  felled  in  the  driest  time  seldom 
contains  less  than  forty  per  cent  (Warington). 

As  to  the  nature  of  the  saline  substances,  reference 
must,  as  has  been  said,  be  made  to  the  "Chemistry  of 
the  Farm  "  and  other  works  for  full  details.  Suffice  it 
here  to  say  that  certain  of  them,  though  always  in  rela- 
tively small  proportions,  are  essential  to  the  life  of  the 
plant ;  certain  others,  generally  met  with,  though  useful, 
are  not  indispensable.  The  former  comprise  salts  of 
potash,  magnesia,  lime,  iron,  and  in  addition  phosphorus 


PLANT  NUTRITION.  17 

and  sulphur.  The  latter  comprise  saltc  of  soda,  silica, 
manganese,  together  with  chlorine  and  occasionally  other 
ingredients. 

Of  the  salts  just  mentioned,  the  nitrates  are  of  extreme 
importance,  inasmuch  as  nitrogen  is  an  essential  con- 
stituent of  protoplasm — without  nitrogen  there  can  be 
no  protoplasm,  without  protoplasm  there  can  be  no  plant. 
The  nitrogen  is  supplied  to  the  plants  from  the  soil  in 
the  form  either  of  nitrates  (potassic  nitrate,  sodic  nitrate), 
or  of  ammonia  salts  in  which  the  nitrogen  is  in  combina- 
tion with  hydrogen.  The  ammonia  in  the  soil  is  made 
to  combine  with  oxygen,  and  thus  to  form  nitric  acid, 
through  the  agency  of  minute  organisms  called  "  Bac- 
teria," which,  like  the  yeast  fungus,  act  as  ferments  ;  and 
by  their  agency  it  is,  as  Mr.  Warington  has  pointed  out, 
in  confirmation  of  the  researches  of  Schloesing  and 
Muntz,  that  the  ammonia  salts,  which  themselves  are 
inert,  or  it  may  be  harmful,  get  converted  into  useful 
nitrates.  Ammonia  salts  applied  to  some  soils  do  no 
good,  because  the  needful  germs  or  ferment  bodies  are 
not  present  in  the  soil ;  but  where  they  do  exist,  they 
convert  the  useless  into  the  useful,  as  before  said.  These 
bacteria  occur  in  all  fermenting  material,  such  as  farm- 
yard dung,  whose  value  as  manure  is  in  part  accounted 
for  by  their  presence  and  agency.  It  is  probable  in  the 
future  that  just  as  the  brewer  uses  his  yeast  to  secure  the 
conversion  of  starch  into  sugar,  and  the  chemist  "seeds" 
his  solutions  to  effect  the  changes  he  wishes  to  bring 
about,  and  just  as  the  gardener  sows  the  spawn  or  germs 
of  mushrooms  in  his  mushroom  bed,  and  obtains  thereby 
a  crop  of  succulent  fungi,  so  the  farmer  may  be  able  to 
apply  to  the  soil  the  ferment-producing  germs  needed  to 
change  its  quality,  and  render  it  available  for  plan^  food. 
When  we  have  arrived  at  that  point,  manuring  will  be 
reduced  to  a  science,  and  a  pinch  of  the  right  material 
will  be  as  efficient  as  a  torn  of  our  present  compounds, 


18  PLANT  LIFE   Otf  THE   FAKM. 

the  large?  part  of  which  are  undoubtedly  wasted  under 
existing  circumstances. 

Potash  salts  are  also  essential,  more  so  in  some  cases 
than  in  others.  At  Rothamsted,  potash,  after  having 
been  employed  for  a  number  of  years  as  a  manure-con- 
stituent on  a  certain  grass  plot,  was  discontinued ;  the 
produce,  in  consequence,  rapidly  declined,  and  the 
quantity  of  carbon  fixed  in  the  tissues  of  the  plants  pro- 
portionately diminished,  although  the  amount  of  nitro- 
gen absorbed  was  the  same  in  the  two  cases.  The  pres- 
ence, therefore,  of  an  adequate  supply  of  potash,  in  the 
soil,  seems  essential  to  the  full  assimilation  of  the  car- 
bon which  is  derived,  as  we  shall  presently  see,  from  the 
air,  in  the  form  of  carbonic  acid  gas.  It  is  believed  from 
recent  experiments  that  without  potash  no  starch  can  be 
formed  ;  and  starch,  as  we  shall  see  hereafter,  is  of 
primary  impoctance  in  the  nutrition  of  the  plant.  In 
any  case  the  value  of  potash  manures  for  increasing  the 
yield  of  certain  crops,  particularly  potatoes,  is  a  fact  be- 
yond dispute. 

Sulphur  and  phosphorus  are  also  derived  from  the 
soil  as  sulphates  and  phosphates.  Both  occur  in  asso- 
ciation with  the  albuminoid  contents  of  the  protoplasm ; 
and  phosphorus  seems  specially  needful  in  the  formation 
of  the  pollen — the  fertilizing  powder  in  the  flowers — and 
in  the  ripening  of  seeds,  while  its  effect  on  the  growth 
of  turnips  is  familiar  to  all  practical  men. 

Iron  is  essential  to  the  formation  of  leaf -green  — 
"  chlorophyll  " — and  chlorophyll  is  essential  to  the  pro- 
duction of  starch  ;  hence  iron  in  some  shape  is  essential 
to  plants,  and  it  also  is  supplied  from  the  soil  in  the 
form  of  saline  solutions. 

What  precise  function  lime  plays  in  the  plant's  economy 
is  not  known ;  but  indirectly  it  is  of  importance  as  a 
means  of  introducing  phosphorus  and  other  essential  in- 
gredients. At  Bothamsted,  in  two  of  the  plots  upon 


PLANT  NUTRITION.  19 

which  barley  has  been  grown  for  thirty  years  in  succes- 
sion, a  mineral  manure  with  nitrogen  has  been  applied  ; 
but  in  the  one  case  lime  has  been  added,  in  the  other 
(otherwise  treated  exactly  in  the  same  way)  no  lime 
has  been  added.  The  plants  on  the  plot  without  the 
lime  are  always  of  a  darker  green  color,  but  they  are  rela- 
tively deficient  in  carbon.  Under  equal  conditions,  it  is 
seen  that  the  amount  of  carbon  assimilated  from  the  at- 
mosphere in  the  -manner  to  be  hereafter  mentioned  is  di- 
rectly dependent  on  the  amount  of  available  nitrogen, 
which  latter  is  derived  from  the  soil — (Lawes  and  Gil- 
bert). 

It.  must  not  be  forgotten  that  the  substances  we  have 
mentioned,  as  well  as  others  not  alluded  to,  though  pos- 
sibly not  directly  concerned  in  the  nutrition  of  the  plant, 
yet  are  so  indirectly  by  causing  changes  in  the  soil,  by 
rendering  some  matters  soluble  and  capable  of  osmotic  ab- 
sorption which  would  not  be  so  without  their  aid,  by 
storing  up  and  preventing  the  waste  of  ingredients  useful 
as  plant  food,  and  so  forth  ;  but  these  matters  pertain 
rather  to  the  physical  and  chemical  history  of  the  soil,  on 
which  account  they  may  be  passed  over  here  without 
further  mention. 

Principles  of  Manuring, — The  few  remarks  we  have 
thought  it  right  to  make  as  to  the  nature  of  the  substances 
absorbed  with  the  water  from  the  soil  have  an  impor- 
tant bearing  on  the  theory  and  practice  of  manuring. 
The  nitrogenous  and  the  saline  substances  are  taken 
from  the  soil,  used  up  in  the  plant,  and  removed  in  the 
crop.  The  annual  produce  of  hay  on  un  manured  land  at 
Rothamsted,  has  been  found  to  be  about  two  thousand 
five  hundred  and  seventy-six  pounds  per  acre,  over  an 
average  of  twenty-five  years,  the  range  of  variation  ac- 
cording to  season  having  been  from  nine  hundred  to  four 
thousand  three  hundred  and  sixty-eight  pounds.  On  the 


20  PLANT   LIFE   OK  THE   FARM. 

other  hand,  the  most  highly  manured  plot  has  yielded 
for  the  same  period  an  average  of  seven  thousand  one 
hundred  and  sixty-eight  pounds  of  hay  per  acre,  varying 
in  separate  years  from  four  thousand  four  hundred  and 
eighty  to  eight  thousand  nine  hundred  and  sixty  pounds, 
according  to  season.  These  figures  will  suffice  to  illus- 
trate the  amount  of  food  derived  from  the  soil  and  from 
the  atmosphere,  and  the  .beneficial  effects  of  suitable  cli- 
matal  conditions.  The  decline  not  only  of  produce,  but 
also  in  mineral  and  nitrogenous  ingredients  in- the  soil, 
in  the  case  of  the  continuously  unmanured  plots  at  Eoth- 
amsted,  is  very  marked.  To  insure  continued  fertility, 
therefore,  and  obviate  exhaustion,  some  restitution  must 
be  made  ;  and  this  is  effected  by  the  addition  at  the  right 
time,  in  the  right  condition,  and  in  the  right  quantities, 
of  an  appropriate  manure  ;  or  the  exhaustion  may  be 
compensated  by  suitable  rotation,  or  the  growth  in  alter- 
nate periods  of  plants  having  different  requirements,  as 
wheat  after  potatoes  or  clover  after  wheat. 

Apparent  Power  of  Selection,  how  Explained,— The 

circumstance  that  certain  crops  are  specially  benefited  by 
particular  manures,  though  they  contain  relatively  little 
of  the  substance  in  their  composition,  would  seem  to  in- 
dicate the  existence  of  a  power  of  selection,  as  also  would 
the  fact  that  plants  of  such  very  different  constitutions 
grow  on  the  same  soil,  but  these  facts  are  better  explained 
by  the  varying  osmotic  conditions  of  the  plants.  Cereal 
crops  and  grasses  generally  are,  for  instance,  specially 
benefited  by  nitrogenous  manures,  though  they  contain 
relatively  little  nitrogen  as  compared  with  clover  and 
other  leguminous  crops,  but  which,  although  they  con- 
tain so  large  a  proportion  of  nitrogen  in  their  constitu- 
tion, are  not  particularly  benefited  by  nitrogenous  ma- 
nures. Beet  roots  and  potatoes,  which  contain  a  con- 
siderable proportion  of  potash  in  their  constitution,  are, 


PLANT  NUTRITIOK.  21 

nevertheless,  not  proportionately  benefited  by  the  appli- 
cation of  potash  manures,  though  they  are  so  to  some 
extent.  These  cases  show  that,  by  virtue  of  the  varying 
osmotic  and  digestive  powers  already  mentioned,  the 
plants  in  question  take  what  they  want,  and  when  they 
want  it,  and  are  not  induced  to  take  more  by  the  addi- 
tion of  larger  supplies.  They  further  show  the  errors 
that  may  arise  from  the  farmer  acting  too  implicitly  on 
the  results  obtained  by  the  chemist  in  the  laboratory.  If 
he  followed  the  indications  of  the  chemist  unchecked  by 
other  experience,  he  would  apply  to  his  land  what  was 
really  not  required  by  the  crop.  Thus  Messrs.  Lawes  and 
Gilbert  tell  us  that  the  exact  composition  of  the  crops  is 
no  direct  guide  to  the  description  and  amount  of  manurial 
constituents  that  will  be  most  effective,  thus  although 
wheat  removes  more  phosphoric  acid  from  the  soil  than 
does  barley,  yet  the  application  of  the  phosphate  is  more 
beneficial  to  the  barley  than  to  the  wheat.  They  con- 
clude, then,  that  it  is  not  necessary  to  supply  to  the  land 
all  the  constituents  that  have  been  removed  from  it,  or 
that  would  be  contained  in  the  crops  it  is  wished  to  grow, 
but  that  we  should  supply  all  or  some,  more  or  less,  ac- 
cording to  circumstances. 


22  PLAtfT  LIFE  OK  THE 

CHAPTER  II. 
NUTRITION   (Continued).— THE    MACHINERY. 

Roots  :  their  nature.— Root-cap.— Root-hairs.— Root  action.— Absorp- 
tion.—Leaves  and  leaf  action. — Chlorophyll. — Absorption  of  fluid 
and  gases. — Leaf  work  by  day  and  by  night. — Oxidation  and  De-oxi- 
dation.— Carnivorous  plants. —  Transpiration. — Circumstances  pro- 
pitious to  it. — The  stem  and  its  work.— Its  characteristics  and  vari- 
eties.— Buds. — Branches. — Tubers. — Bulbs. — Uses  of  the  stem. — As- 
cent of  liquids. — Sap  currents. 

Roots  :  Their  Nature,  Etc. — So  far  as  regards  the  ab- 
sorption of  those  food  materials  derived  from  the  soil  by 
the  means  above-mentioned,  the  root  and  its  sub-divisions 
are  the  agents  through  which  the  absorption  takes  place. 
It  is  not  necessary  to  allude  to  the  various  forms  and 
modifications  of  roots  which  form  the  study  of  the  bot- 
anist further  than  to  say  that  their  manifold  differences 
of  form  depend  chiefly  on  the  relative  proportion  that 
the  body  of  the  root  bears  to  its  branches.  If,  as  in  a 
"  tap-root,"  like  a  carrot,  the  body  is  large,  the  branches 
are  small;  if,  as  in  the  "fibrous  root"  of  a  grass,  the 
body  is  small,  the  branches  are  numerous  and  long. 

In  ordinary  language  a  great  many  things  are  called 
roots  which  are  not  strictly  so.  For  most  people  all  parts 
of  the  plant  situate  below  the  surface  of  the  ground  are 
roots  or  portions  of  roots.  Botanists,  having  regard 
alike  to  the  origin,  mode  of  growth,  structure,  and  uses 
of  roots,  are  enabled  to  define  roots  partly  by  positive, 
partly  by  negative  characters.  Thus  roots  originate  be- 
neath the  surface,  that  is  from  within  the  tissues  of  the 
plant  (endogenous),  and  force  their  way  out  through  the 
rind,  as  contrasted  with  branches  and  leaves  which  orig- 
inate on  the  surface  (exogenous).  The  extreme  tip  of 
the  root,  and  of  its  sub-divisions,  is  furnished  with  a  mi- 
nute "  root-cap  "  of  dead  tissue  pushed  off  from  the  tip 


PLANT  HTTTKITIOH.  23 

as  it  grows,  as  the  feathers  of  a  bird  are  removed  during 
the  moulting  season.  No  such  cap  exists  at  the  end  of  a 
branch  or  leaf.  Again,  while  it  is  the  office  of  a  stem  or 
branch  to  produce  leaves  or  scales,  which  are  the  repre- 
sentatives of  leaves,  no  root  proper,  as  a  rule,  produces 
leaves  or  flowers. 

Botanists  make  a  distinction  between  "true  roots" — 
which  are  the  direct  outgrowth  from  the  original  "  rad- 
icle "  of  the  germinating  seedling,  and,  in  fact  constitute 
its  direct  continuation — and  "  adventitious  "  roots,  which 
spring  from  the  stem  and  branches,  and  which  are  only 
indirectly  derived  from  the  primary  root.  For  our  pres- 
ent purpose  the  distinction  is  unimportant. 

The  root  of  a  plant  and  its  branches  have  different 
forms  and  subserve  different  purposes.  Whatever  food  is 
taken  up  from  the  soil  is  taken  up  by  them.  They  act 
as  stays  and  holdfasts,  they  serve  as  storehouses  of  nour- 
ishment. Their  form  varies  according  to  their  use,  their 
needs,  the  competition  with  other  roots,  the  conditions 
under  which  they  have  to  grow,  and  other  circumstances, 
not  forgetting  the  heritage  bequeathed  to  them  by  their 
predecessors  from  generation  to  generation,  for,  like  all 
parts  of  the  plant — like  the  plant  itself — the  root  is  the 
product  of  what  has  gone  before,  adapted  and  modified 
by  the  exigencies  of  the  present. 

In  this  place  we  have  to  consider  the  roots  chiefly  in 
their  character  as  absorbent  organs.  The  one  function 
common  to  all  roots  is  absorption.  They  may  have  other 
offices  to  fulfil,  and  they  have  very  varied  forms ;  but 
when  we  come  to  consider  the  main  function  of  the  root, 
then  we  find  simplicity  and  relative  uniformity  of  struc- 
ture. The  thick,  woody  limb  of  an  elm  root,  as  we  see 
it  exposed  in  a  hedge-bank  from  which  the  soil  has  fallen, 
is  no  organ  of  absorption  ;  the  thick  "  bulbs  "  (so-called) 
of  a  turnip  or  a  beet,  are  not  organs  of  absorption  ; 
neither  are  these  latter,  any  more  than  the  tubers  of  po- 


24  PLAKT  LIFE  OK  THE  FAEK. 

tatoes,  stri'ctly  speaking,  roots.  Our  best  and  truest  con- 
ception of  a  root  as  an  organ  of  absorption  is  that  of  a 
single  fibril  or  of  a  dense  mass  of  the  finest  fibrils — root- 
branches  no  thicker  than  a  hair.  These  fibrils  grow  in 
length  close  to  their  tips,  the  actual  tip  being  covered 
with  a  thin  extinguisher-like  cap  of  dead  tissue — the  root- 
cap  already  mentioned,  and  which  serves  as  a  shield  to 
the  softer  tissues  within.  The  structure  is  of  the  sim- 
plest, merely  layers  of  cells  such  as  before  described, 
arranged  in  more  or  less  longitudinal  ranks,  the  cells 
themselves  delicate  and  thin- walled.  The  fineness  of  the 
root-fibril,  its  growth  near  the  tip,  its  wonderful  power 
of  motion,  are  all  well  adapted  to  permit  of  the  fibril 
ma*king  its  way  between  the  particles  of  soil,  and  extract- 
ing nourishment  from  the  fluid  surrounding  them.  We 
have  only  to  examine  the  root  of  a  wheat  plant,  or  still 
better  of  a  perennial  pasture  grass,  to  see  how  perfectly 
this  is  accomplished.  Under  such  circumstances  the 
root-fibrils  form  a  dense  wig,  as  it  were,  of  feeding 
threads  which  occupy  the  soil  so  thoroughly  that  the  soil 
is  held  together  by  them.  It  is  easy  to  see  that  although 
the  absorbent  power  of  each  thread  is  infinitesimal,  yet 
in  the  aggregate  it  must  be  very  large.  Fine  as  they 
often  are,  these  root-fibrils  are  very  frequently,  but  not 
always,  provided  with  yet  finer  "  root-hairs."  These  are 
extremely  minute  threads  emerging  from  the  superficial 
cells  of  the  root,  in  the  vicinity  of,  but  not  exactly  at, 
their  tips.  When  their  growth  is  stimulated  by  the 
presence  of  moisture  or  suitable  plant  food,  they  often 
occur  in  such  numbers  as  to  form  a  dense  cobweb-like 
investment  to  the  roots. 

Root  Action— What  the  Roots  do.— It  has  been  proved 
by  repeated  experiments  that  the  absorption  of  liquid  food 
(no  solid  matter  can  in  any  case  be  absorbed)  takes  place 
towards  the  lower  end  of  the  root-fibrils,  and  by  means 


PLANT  NTTTKITION.  25 

of  these  root-hairs  when  they  are  present.  The  upper 
portions  of  the  fibril  do  not  act  as  absorbent  organs,  the 
root  hairs  do  not  exist  in  this  part  of  the  root,  the  struc- 
ture of  which  becomes  gradually  less  and  less  adapted 
for  absorption,  so  that  the  actual  space  in  each  fibril  de- 
voted to  absorption  is  relatively  small  in  relation  to  its 
length.  The  remainder  of  the  fibril  acts  as  a  conduit  for 
the  transmission  of  the  absorbed  fluids  upward  from  cell 
to  cell  by  osmosis  and  imbibition,  and  as  a  holdfast. 

The  passage  of  the  insoluble  matters  in  the  soil  into 
the  root  is  effected  by  an  acid  liquid  produced  by  the 
root-hair  or  cell  in  consequence  of  its  contact  with  the 
particle  of  soil,  aided  by  the  water  in  the  soil.  This  acid 
fluid  saturates  the  cell  walls,  corrodes,  and  effects  the 
solution  of  the  surface  of  the  particle  of  the  soil  in  con- 
tact with  the  fibril  or  root-hair.  No  passage  of  acid  fluid 
out  of  the  cell  takes  place,  root  excretions  having  no  ex- 
istence ;  but  the  corrosive,  and  as  it  were  digestive,  action 
above  mentioned,  is  due  solely  to  the  absolute  contact  of 
the  cell  of  the  root  with  the  particle  of  the  soil. 

The  soil,  therefore,  is  not  to  be  looked  on  as  contain- 
ing so  much  liquid  food  ready  for  instant  use  ;  that  may 
be  so  as  regards  water,  but  for  other  substances  the  di- 
gestive action  of  the  roots  is  necessary. 

In  addition  to  the  absorption  of  liquids  as  just  detailed, 
roots  have  the  power  of  freely  absorbing  the  oxygen  gas 
contained  in  the  soil,  and  if  a  supply  of  oxygen  be  cut 
off,  the  roots  die  from  suffocation.  One  use,  therefore, 
of  the  plowing  and  harrowing  operations  is  to  keep  the 
soil  open  and  permeable,  and  thus  allow  the  access  of  oxy- 
gen to  the  roots. 

On  the  other  hand,  roots  do  not  absorb  carbonic  acid 

gas  nor  exhale  oxygen  as  the  leaves  do — in  the  sunlight 

—but  they  do  give  off  carbonic  acid  gas,  which,  with  the 

aid  of  water,  converts  the  insoluble  carbonates  of  the  soil 

2 


26  PLANT  LIFE  ON  THE  FARM. 

into  soluble  bicarbonates,  and  exercises  a  similar  power 
of  solution  in  the  case  of  phosphates. 

Leaves  and  Leaf  Action. — The  two  great  factors  in 
the  feeding  of  the  plant  are  the  roots  and  the  leaves. 
The  soil  supplies  to  the  roots,  as  we  have  seen,  water  in 
large  quantities,  gases,  earthly  and  saline  substances  ; 
but  the  air  is  an  equally  important  source  of  nourish- 
ment, or  even  more  so,  since  there  are  rootless  plants, 
and  plants  which  receive  no  part  of  their  food  directly 
from  the  soil,  while  no  plant  can  exist  without  air,  and 
no  plant  that  is  of  direct  importance  to  the  cultivator 
can  live  without  light.  We  insert  the  word  "  direct " 
because  there  is  a  whole  group  of  plants  which  can  thrive 
in  the  absence  of  light,  but  these  form  no  part  of  the 
ordinary  crops  of  a  farm.  Indirectly,  however,  as  has 
been  pointed  out,  in  considering  the  agency  of  bacteria 
as  ferments  in  the  soil,  these  organisms  to  whose  career 
light  is  not  essential  may  be  of  the  greatest  consequence 
to  cultivators  ;  and  it  is  probable  that  the  future  will 
show  us  much  more  fully  how  great  is  our  indebtedness 
to  them.  For  our  present  purpose,  we  have  to  deal  with 
plants  producing  leaves,  to  point  out  some  of  the  work 
which  the  leaves  do,  and  to  give  some  indication  of  how 
they  do  it. 

Unlike  the  root,  which  originates  from  within  the  sub- 
stance of  the  plant  and  breaks  its  way  out  to  the  surface, 
the  leaf,  as  has  been  stated,  is  a  direct  production  from 
the  surface  of  the  stem  or  branch.  It  is  one  of  the  char- 
acteristics of  a  root  not  to  produce  leaves  ;  it  is  one  of  the 
attributes  of  the  stem  and  its  subdivisions  to  clothe 
themselves  with  these  appendages. 

In  form,  texture,  size.,  the  leaf  presents  infinite  variety. 
Sometimes  it  is  a  mere  dry  scale,  sometimes  a  thick, 
fleshy  excrescence ;  now  it  offers  a  broad,  banner-like 
surface,  now  it  is  reduced  to  the  form  and  dimensions  of 


PLANT  NUTRITION.  27 

a  needle.  Sometimes  it  is  all  in  one  piece,  the  e<  blade  " 
being  unbroken  at  the  edge,  or  variously  notched  and 
indented ;  at  other  times  the  blade  is  made  up  of  few  or 
of  an  infinite  number  of  separate  segments  or  leaflets. 
If  the  blade  is  in  one  piece,  it  is  "  simple,"  as  the  leaf  of 
wheat ;  if  in  many  pieces,  as  the  leaf  of  clover,  sainfoin, 
or  tares,  it  is  "compound."  Very  often  it  has  a  stalk 
or  "  petiole,"  sometimes  it  has  none.  Sometimes  it  has 
appendages  at  its  base  called  "  stipules,"  well  seen  in 
vetches  or  clover  ;  while  the  leaves  of  all  grasses,  includ- 
ing all  the  cereals,  are  provided  with  a  little  mem- 
branous tongue  or  outgrowth  from  the  junction  of  the 
sheathing  stalk  of  the  leaf  with  the  blade,  whicli  is  called 
a  "ligule,"  and  which,  though  often  overlooked,  is  of 
some  moment  to  the  grazing  farmer,  as  affording  one 
means  of  distinguishing  useful  from  useless  grasses. 
Further  than  this  we  need  not  go  at  present  in  speaking 
of  the  form  and  general  appearance  of  leaves.  Nor  need 
we  enter  very  deeply  into  the  minutiae  of  their  structure. 
All  ordinary  leaves  are  flat  plates  of  cells  of  various 
shapes  variously  arranged,  and  traversed  by  fibrous  bun- 
dles. These  bundles  consist  of  long,  tapering  cells  or 
fibres  filled  with  woody  or  other  matter,  and  of  rows  of 
similar  cells  placed  end  to  end  in  rows,  the  partitions 
between  the  cells  being  removed,  so  that  they  form  con- 
tinuous tubes.  There  are  many  kinds  of  "vessels,"  but 
all  of  them  originate  from  cells.  The  fibro- vascular 
bundles,  with  their  wood-cells,  bast-cells,  and  vessels, 
constitute  what  are  commonly  termed  the  veins  of  the 
leaf.  Covering  over  this  mass  of  cells  and  vessels  is  a 
skin  or  epidermis,  consisting  of  flattened  cells  usually 
placed  in  accurate  contact  on  the  upper  surface  of  the 
leaf,  but  below,  so  modified  in  shape  and  position  as  to 
leave  a  number  of  pores  or  openings  called  "stomata," 
the  number,  arrangement,  size,  and  form  of  which  vary 
very  much  in  different  plants  ;  suffice  it  here  to  say  that 


28  PLANT  LIFE  otf  THE  FARM. 

they  are  in  general  very  numerous.  So  far,  then,  there 
is  little  difference  to  be  noted  between  the  structural 
elements  of  a  leaf  and  those  of  a  root.  The  root  is  more 
or  less  cylindric,  the  leaf  is  more  or  less  flat ;  but  the  es- 
sential structures,  though  differently  arranged,  are  pretty 
much  the  same,  with  one  or  two  notable  exceptions. 
The  root  has  no  breathing  pores  or  stomata,  and  the 
contents  of  its  constituent  cells  are  so  far  different  from 
those  of  the  leaves  that  they  contain  no  green  coloring 
matter. 

Chlorophyll. — The  main  and  specially  important  char- 
acteristic of  the  leaf  (and  of  all  the  green  parts  of  plants), 
so  far  as  their  life-work  is  concerned,  is  the  presence  in 
the  cells  of  the  green  matter  called  "chlorophyll." 
With  and  by  its  agency  the  leaf  can  do  work  impossible 
to  be  done  otherwise ;  work,  the  measure  of  which  de- 
termines the  health  and  vigor  of  the  plant,  the  default 
of  which  ensures  its  death.  It  is  true  that  chemists  and 
physicists  have  not  yet  unravelled  all  the  mysteries  of 
chlorophyll,  and  there  remains  a  doubt  whether  it  is  the 
potent  agent  it  has  hitherto  been  supposed  to  be,  or 
whether  the  power  does  not  reside  in  some  other  agent 
mixed  with  it.  Into  these  questions  we  cannot  here 
enter.  Whatever  be  the  actual  truth  of  the  matter,  the 
transcendent  importance  of  chlorophyll,  and  of  all  that 
its  presence  implies,  is  universally  admitted.  It  must 
suffice  to  say  that  chlorophyll  is  a  green,  waxy  substance, 
occurring  in  certain  of  the  cells  mixed  with  their  proto- 
plasmic contents.  In  amount  and  appearance  it  varies  in 
different  cases  and  under  varying  circumstances.  It 
does  not  occur  in  all  the  cells  of  the  leaf,  but  chiefly  or 
only  in  those  on  the  upper  surface,  and  which  are  there- 
fore the  most  directly  exposed  to  the  action  of  the  rays 
of  the  sun. 


PLANT  NUTRITION.  29 

Feeding  by  Leaves. — We  are  now  in  a  position  to 
understand  the  nutritive  process  as  it  is  carried  on  by 
the  leaves,  and  our  first  enquiry  is  as  to  what  they  feed 
on — what  is  the  nature  of  the  food  they  take  in  ?  In 
the  first  place,  it  is  clear  that  they  can  take  in  no  solid 
matter.  The  pores  or  stomata  already  alluded  to  are  the 
only  openings  by  which  such  matter  could  get  into  the 
interior  of  the  leaf  ;  and  we  know,  from  experience,  that 
if  these  pores  get  blocked,  the  leaf  suffers  rather  than 
£ains.  Moreover,  the  cells,  bounding  the  aperture,  open 
and  close  according  to  the  condition  of  moisture  of  the 
atmosphere,  and  at  any  rate,  when  closed,  they  could 
admit  no  solid  matter. 

Absorption  of  Water. — As  to  fluids,  it  is  proved  that 
leaves,  under  certain  circumstances,  and  when  there  is 
no  structural  provision  to  prevent  it  (as  there  often  is) 
can  and  do  absorb,  not  only  watery  vapor,  but  the  fluid 
itself.  This  happens  more  especially  when  the  plant  is 
flagging  from  the  rapid  exhalation  of  moisture,  and  from 
deficient  root  supply,  and  it  affords  an  explanation  of 
the  benefit  plants  derive  from  the  deposit  of  dew  after  a 
hot  and  drying  day.  Still,  the  absorption  of  water  by 
means  of  the  root  seems  to  be  generally  of  more  conse- 
quence than  that  by  the  leaf,  so  that  the  entrance  of 
water  by  the  leaf  may,  for  our  purposes,  be  passed  over 
without  further  mention. 

Absorption  and  Exhalation  of  Gases. — There  remains 
gaseous  food.  It  has  been  shown  that  the  root  absorbs 
gases,  as  oxygen  ;  but  in  this  respect,  as  also  in  the  ab- 
sorption of  other  gases,  the  root  is  surpassed  by  the  leaf. 
The  paramount  function  of  the  leaf  is  the  absorption  and 
assimilation  of  carbon.  Carbon,  as  such,  does  not  exist 
in  the  atmosphere,  unless,  indeed,  as  an  impurity  in  the 
air  of  towns?  and  a  very  prejudicial  one  to  plants.  It  is 


30  PLANT  LIFE   ON  THE  FARM. 

in  the  form  of  carbonic  acid  gas — a  combination  of  car- 
bon and  oxygen — that  it  is  found  in  the  atmosphere,  but 
only  in  small  proportion  compared  with  the  other  con- 
stituents. In  the  plant  carbon  exists  in  much  larger 
proportion  than  any  other  ingredient,  with  the  sole  ex- 
ception of  water.  It  forms,  in  fact,  about  fifty  per  cent 
of  the  dry  matter  of  plants  left  behind  after  the  water 
and  gases  have  been  expelled  by  heat.  This  large 
quantity  of  carbon  has  to  be  taken  up  in  the  form  of 
carbonic  acid  by  the  leaves.  It  is  a  moot  point  whether 
any  carbon  is  taken  up  by  the  roots,  but,  if  any,  it  is 
only  a  small  proportion.  In  any  given  volume  or  quantity 
of  air,  the  proportion  of  carbonic  acid  is  very  minute,  so 
that  the  leaves  must  be  very  active  in  securing  and  util- 
izing all  that  comes  within  their  reach. 

What  Leaves  do  in  the  Light, — Direct  experiments 
have  shown  that  this  appropriation  of  carbonic  acid  is 
effected  by  the  agency  of  the  green  coloring  matter  or 
chlorophyll  when  exposed  to  the  action  of  light.  In  the 
dark  no  such  appropriation  takes  place.  The  plant  feeds, 
so  far  as  its  carbon  is  concerned,  on  the  carbonic  acid  of 
the  air  through  the  agency  of  sunlight  and  of  chlorophyll. 
At  least  two-thirds  of  the  chlorophyll  itself  consists  of 
carbon  in  association  with  a  small  proportion  of  oxygen 
and  hydrogen,  and  a  still  smaller  quantity  of  nitrogen. 
The  carbonic  acid  thus  introduced  into  the  plant 
does  not  remain  as  such,  but  its  constituent  carbon  is 
retained  in  the  plant  for  its  own  purposes,  while  the 
oxygen  gas  is  eliminated.  The  bubbles  of  gas  that  rise 
from  a  water  weed  in  a  pond  when  exposed  to  the  sun 
consist  of  oxygen  chiefly,  and  it  has  been  shown  that  the 
amount  of  oxygen  gas  given  off  is  about  equal  to  that  of 
the  carbonic  acid  gas  absorbed.  Hydrogen  and  oxygen, 
the  absorbed  water,  are,  it  is  said,  assimilated  by  the 
plant  simultaneously  with  the  carbon. 


PLANT  HUTKITION.  31 

The  first  icsult  of  this  assimilation,  chemists  tell  us,  is 
the  formation  of  a  soluble  substance,  "  glucose,"  allied 
both  to  starch  and  to  sugar,  and  which,  or  a  portion  of 
which,  becomes  starch,  and  is  stored  up  for  future  use  in 
that  form.  No  starch  is  formed  in  an  atmosphere  pur- 
posely deprived  of  carbonic  acid  by  the  experimenter, 
even  if  the  cell  be  exposed  to  the  light.  Moreover,  any 
starch  that  may  have  been  previously  formed  disappears 
under  such  circumstances,  just  as  it  would  do  in  dark- 
ness, where  the  plant  is  dependent  on  its  reserve  stores 
for  its  nourishment,  and  not  on  those  which  it  procures 
directly  for  itself  when  exposed  to  light  in  an  atmosphere 
in  which  carbonic  acid  gas  forms  a  part.  The  changes 
in  question  are  presumed  to  take  place,  not  in  the  pro- 
toplasm itself,  but  in  the  chlorophyll  grains ;  at  any  rate, 
it  is  in  them  that  the  starch  first  makes  its  appearance. 
It  is  certain,  also,  that  only  cells  which  contain  chlor- 
ophyll—  and  then  only  when  exposed  to  light — can 
directly  assimilate  carbon.  Cells  without  chlorophyll, 
such  as  those  of  fungi,  obtain  their  carbon  by  more  indi- 
rect and  complex  means.  The  vital  importance  of  the 
exposure  of  the  leaves  to  sunlight  might  be  inferred  from 
the  bending  of  the  stems  and  branches  to  the  light,  and 
placing  of  the  mobile  leaves  at  such  an  angle  as  to  receive 
the  full  benefit  of  the  sun's  rays — matters  which  will  be 
spoken  of  further  on. 

What  the  Leaves  do  in  Darkness.— Inhalation  of 
Oxygen. — In  darkness  (as  well  as  under  the  influence  of 
light,  in  the  case  of  those  cells  that  do  not  contain  chlo- 
rophyll) changes  go  on  of  a  different  character  to  those 
just  described.  There  is,  in  fact,  a  constant  elimination 
of  carbonic  acid  gas,  and  a  corresponding  absorption  and 
retention  of  oxygen  gas.  The  interchange  of  these  gases 
has  been  compared  to  the  corresponding  changes  in  the 
case  of  the  respiration  of  animals  ;  but  doubts  have  been 


32  PLANT  LIFE   ON  THE   FAEM. 

thrown  on  the  existence  of  any  direct  connection  between 
the  absorption  of  oxygen  and  the  emission  of  carbonic 
acid,  in  plants,  because  it  has  been  shown  that  a  green 
leaf  placed  in  darkness  and  in  an  atmosphere  deprived  of 
oxygen  nevertheless  exhales  carbonic  acid,  the  emission 
of  which  under  such  circumstances  cannot  of  course  be 
connected  with  any  corresponding  inhalation  of  oxygen. 

Though  going  on  constantly,  the  energy  of  the  oxi- 
dizing process  is  much  less  than  that  of  the  opposite  de- 
oxidizing process,  carried  on  when  the  chlorophyll  cells 
are  exposed  to  the  light.  Deprived  of  oxygen,  the  move- 
ments of  the  protoplasm,  the  movements  of. the  roots 
and  of  the  leaves  cease,  other  manifestations  of  activity 
are  put  a  stop  to,  and  the  plant  dies  of  suffocation. 
Moreover,  it  has  been  shown  that  each  cell  consumes  its 
own  supply  of  oxygen,  and  if  that  fails  it  will  die,  even 
though  adjoining  cells  be  provided  with  the  gas.  In  this 
particular  then  the  cells  act,  not  in  concert,  but  indi- 
vidually (Van  Tieghem).  It  is  not  essential  that  the 
oxygen  should  be  in  a  free  state  ;  it  may  be  utilized  by 
plants  from  a  compound  containing  oxygen,  and  from 
which  it  may  easily  be  obtained.  An  instance  of  this  is 
afforded  in  the  case  of  the  disease  of  animals  known  as 
"  charbon,"  which  is  now  known  to  be  caused  by  the 
existence  in  the  blood  of  the  animal  affected  of  a  micro- 
scopic plant  (Bacillus  anthracis),  which  lives  in  the  blood, 
and  which,  not  finding  sufficient  oxygen  in  its  serum  or 
liquid  portion,  decomposes  the  matter  contained  in  the 
red  corpuscles  and  utilizes  the  oxygen  they  afford.  To 
live  itself,  it  deprives  the  creature  in  which  it  is  estab- 
lished of  its  oxygen,  and  thus  not  only  kills  it  by  suffo- 
cation, but  eventually  cuts  off  its  own  supply  of  food. 

The  effect  of  depriving  a  plant  which  contains  glucose 
of  its  oxygen  is  to  convert  that  glucose  into  alcohol. 
Thus  fermented  liquors,  such  as  beer,  wine,  etc.,  owe 
the  alcohol  they  contain  to  the  temporary  cutting  off  of 


PLANT   NUTRITION.  33 

the  supply  of  oxygen  to  the  ferment,  in  consequence  of 
which  the  glucose  they  contain  becomes  converted  into 
alcohol. 

Carnivorous  Plants,  Parasites, — The  leaves  of  certain 
plants  are  endowed  under  certain  circumstances  with  a 
power  of  digesting  and  absorbing  animal  substances 
placed  in  contact  with  them.  When  a  minute  fragment 
of  meat,  for  instance,  is  placed  upon  the  leaf  of  a  drosera, 
or  sundew,  the  tentacle-like  glandular  hairs  of  the  plant 
bend  over  to  grasp  the  intruding  morsel,  a  peculiar  di- 
gestive fluid  is  formed  as  a  result  of  the  contact — just  as 
the  gastric  juice  in  the  human  stomach  is  secreted  when 
food  enters  that  organ — and  this  fluid  effects  the  solution 
of  the  meat,  the  nutritive  solution  so  formed  being 
absorbed  and  applied  to  the  benefit  of  the  plant.  To 
common  observation  the  actual  gain  to  the  plant  by  this 
method  of  feeding  may  appear  slight,  or  even  none  ;  but 
the  more  delicate  tests  applied  by  the  botanist  have 
sufficed  to  prove,  not  only  that  the  processes  just 
mentioned  really  do  go  on,  but  also  that  they  are  ben- 
eficial to  the  plant,  and  contribute  to  the  formation  of 
more  numerous  and  more  robust  seedlings.  The  ration- 
ale of  this  mode  of  obtaining  nutrition  seems  somewhat 
analogous  to  that  in  the  root,  where  also  the  acid  fluid 
with  which  the  cell-wall  is  permeated,  when  it  comes 
into  contact  with  the  particles  of  soil,  determines  their 
solution  and  renders  them  fit  for  absorption  into  the 
plant.  Practically  this  admittedly  exceptional  mode  of 
nutrition  by  the  leaf  might  seem  of  little  moment,  but  it 
is  probable  that  in  the  future  direct  nutrition  by  this 
means  will  be  shown  to  be  of  much  greater  importance 
than  it  appears  to  be  at  present.  In  any  case,  the  fact 
that  ammonia-solutions  and  ammonia-vapors  are  absorbed 
by  leaves  with  increased  manifestations  of  vital  activity, 
renders  this  mode  of  feeding  a  matter  of  some  conse- 


34  PLANT  LIFE   ON  THE   FAKM. 

quence  to  the  agriculturist ;  and  the  escape  of  ammoni- 
acal  vapor  from  the  muck-heap  may  not  after  all  be  the 
wasteful  operation  it  is  usually  supposed  to  be — that  is, 
if  the  circumstances  are  such  that  plants  can  avail  them- 
selves of  the  exhaled  vapor. 

It  is  a  very  remarkable  fact  that  fluids  which  do  not 
contain  nitrogen  do  not  give  rise  to  the  movements  of 
the  leaves,  the  changes  in  the  protoplasm,  the  formation 
of  a  digestive  fluid,  and  other  consequences,  which  Darwin 
has  discussed  in  his  work  on  "Insectivorous  Plants." 
Mere  mechanical  irritation  of  the  leaves  is  not  sufficient 
to  ensure  the  formation  of  the  ferment  requisite  for 
digestion.  The  different  effects  of  salts  of  soda  and  of 
potash,  in  the  case  of  the  leaves  of  drosera,  are  also  sug- 
gestive, for  while  soda-salts  give  rise  to  the  physiological 
activity  in  the  leaves,  potash  salts  do  not  do  so,  and  some 
of  them  are  even  poisonous.  Neither  the  one  nor  the 
other  is  poisonous  to  the  roots,  unless  applied  in  very 
large  quantities.  Phosphate  of  ammonia  and  phosphate 
of  soda  act  with  remarkable  vigor  on  the  leaves,  while 
phosphate  of  potash  is  quite  inert,  the  activity  in  the 
former  cases  being  probably  due  to  the  phosphorus. 

It  would  thus  appear  that  while  almost  all  plants  ab- 
sorb the  inorganic  elements,  including  their  nitrogen, 
from  the  soil,  and  derive  their  carbon  from  the  atmos- 
phere, there  are  others,  such  as  drosera,  which  digest  and 
absorb  nitrogenous  matters  by  means  of  their  leaves. 
Such  plants  can  even  extract  nitrogenous  matter  from 
pollen,  seeds,  and  bits  of  leaves  (Darwin).  Other  plants 
absorb  ammonia  by  means  of  the  hairs  covering  their 
leaves,  and  this  class  is  probably  more  numerous  than 
the  foregoing.  Others,  again,  have  no  faculty  of  digest- 
ing by  their  leaves,  though  they  absorb  solutions  of 
decaying  animal  matter  by  their  means.  Some,  such  as 
the  bird's  nest  orchis,  feed  on  the  decay  of  vegetable 
matter,  and  are  themselves  nearly  or  quite  destitute  of 


PLANT  NUTRITION.  35 

chlorophyll.  Lastly,  there  is  the  class  of  true  parasites, 
such  as  the  broom-rapes  ( Orobanche)  and  dodders  ( Cus- 
cuta),  which  affix  themselves  to  living  plants,  and  being 
themselves  destitute  of  chlorophyll,  are  unable  to  live, 
except  at  the  expense  of  the  plants  upon  which  they 
grow. 

Transpiration  of  Water, — There  is  a  large  absorption 
of  water,  as  has  been  said,  by  means  of  the  root,  and  in 
some  cases,  at  any  rate,  there  is  an  absorption  of  the 
same  fluid  or  vapor  by  means  of  the  leaves.  On  the  other 
hand,  there  is  a  loss  of  water  or  watery  vapor  from  the 
surface,  which  is  sometimes  so  profuse  as  to  cause  the 
plant  to  wither  and  flag.  We  have  only  to  place  some 
leaves  in  a  cool  tumbler,  and  expose  them  to  the  light, 
to  see  the  condensed  water  on  the  sides  of  the  glass. 
The  quantity  of  watery  vapor  emitted  in  sunlight  by  the 
green  surfaces  of  plants  is  enormous,  and  it  has  been 
shown  experimentally  that  it  is  the  chlorophyll  which  is 
largely  concerned  in  this  outflow,  for  where  that  sub- 
stance is  deficient  and  wanting,  transpiration  of  fluid  is 
proportionately  reduced  or  stopped.  But  while  bright 
light,  such  as  that  furnished  by  the  red  and  yellow  ray 
of  the  solar  spectrum,  is  most  efficacious  in  stimulating 
the  decomposition  of  carbonic  acid,  it  is  the  blue  ray 
which  specially  favors  transpiration  of  the  fluid.  A  high 
degree  of  temperature,  as  might  be  expected,  favors 
transpiration,  as  does  also  a  dry  state  of  the  atmosphere. 
The  condition  of  the  plant,  its  age,  and  other  circum- 
stances are  also  important  agents  in  regulating  the 
amount  of  transpiration. 

Some  idea  of  the  amount  of  water  given  off  may  be 
gleaned  from  some  experiments  made  by  Sir  JohnLawes, 
and  recorded  in  the  " Journal"  of  the  Horticultural 
Society  for  1850,  thus — During  one  hundred  and  seventy- 
two  days,  March  19  to  September  7,  the  total  weight  of 


36  PLANT   LIFE   ON   THE   FAKM. 

water  given  off  from  small  flower  pots  containing  plants, 
grown  without  manure,  was  as  follows  : — 

Grains. 

Wheat 112,527 

Barley 120,025 

Beans , . 112,231 

Peas 109,082 

or,  say,  an  average  loss  for  each  pot  for  the  whole  period 
of  over  one  hundred  thousand  grains.  To  show  the  effect 
of  the  season,  it  may  be  said  that  the  average  daily  loss  in 
grains  in  the  case  of  flower  pots  containing  plants  of 
wheat  grown  in  unmanured  soil,  was  : 

Grains. 

March  19  to  28 . . : 14.3 

March  28  to  April  28 40.9 

April  28  to  May  25 162.4 

May  25  to  June  28 1177.4 

June  28  to  July  28 1535.3 

July  28  to  August  11 1101.4 

August  11  to  September  7 230.9 

Barley  lost  more  in  April  and  May  than  the  wheat, 
and  more  also  in  July  and  August.  Beans  lost  much 
less  than  either  of  the  cereals,  the  amount  increasing 
regularly  to  June  to  July,  and  diminishing  in  August. 
Peas  evaporated  less  than  beans,  especially  in  June.  The 
results  obtained  from  the  plants  grown  with  various  ma- 
nures were  less  uniform,  and  need  not  here  be  cited,  the 
object  being  merely  to  illustrate  the  large  quantity  of 
water  evaporated  and  its  gradual  increase  with  the  de- 
velopment and  growth  of  the  plant  and  the  advance  of 
the  season.  While  the  precise  effect  of  any  particular 
manure  in  promoting  either  absorption  or  transpiration 
is  not  fully  known,  it  has  been  shown  that  the  alternate 
use  of  pure  water  and  of  manure  water  has  resulted  in  a 
large  proportionate  amount  of  water  being  absorbed  and 
transpired  by  the  plant,  and  a  greater  development  of 
the  plant  than  is  the  case  where  either  fluid  is  applied 
alone  (Vesque). 


PLANT   NUTRITION.  37 

Summary. — The  main  functions  of  the  leaf  may,  there- 
fore, be  stated  to  be  the  reception  and  emission  of  gases 
— now  this,  now  that,  according  as  it  is  exposed  to  light 
or  darkness — and  the  absorption  and  emission  of  watery 
vapor.  The  result  of  all  these  varied  processes  now  act- 
ing together  and  in  unison — at  other  times  in  antagonism 
as  it  were — is  the  nutrition  of  the  plant,  the  building  up 
of  its  structure,  the  formation  of  most  of  those  ingre- 
dients which  render  a  plant  sightly  or  useful.  The  im- 
portance of  these  processes  may  be  summed  up  in  the 
words  of  an  eminent  physiologist  ("  Gardeners'  Chroni- 
cle," 1881,  Feb.  5,  p.  169)  :— "  All  the  labor  of  the 
plant  by  which  out  of  air,  water,  and  a  pinch  of  divers 
salts  scattered  in  the  soil,  it  builds  up  leaf  and  stem  and 
roots,  and  puts  together  material  for  seed  or  bud  or 
bulb,  is  wrought  and  wrought  only  by  the  green  cells 
which  give  greenness  to  leaf  and  branch  or  stem.  .  .  . 
We  may  say  of  the  plant  that  the  green  cells  of  the  green 
leaves  are  the  blood  thereof.  As  the  food  which  an 
animal  takes  remains  a  mere  burden  until  it  is  transmut- 
ed into  blood,  so  the  material  which  the  roots  bring  to 
the  plant  is  mere  dead  food  until  the  cunning  toil  of  a 
chlorophyll-holding  cell  has  passed  into  it  the  quickening 
sunbeam.  Take  away  from  a  plant  even  so  much  as  a 
single  green  leaf,  and  you  rob  it  of  so  much  of  its  very 
life  blood."  A  warning  this  against  the  premature  re- 
moval of  leaves,  as  when  leaves  are  taken  from  the  bulbs 
of  our  mangels  before  they  have  completed  their  work  of 
formation  and  accumulation. 

In  this,  and  other  matters,  however,  the  cultivator 
often  has  to  make  a  compromise,  and  act  as  is  best  for 
himself  under  the  particular  circumstances  of  the  time. 
It  is  not  the  good  of  the  plant  that  he  seeks  in  the  first 
instance,  but  only  in  so  far  as  it  contributes  to  his  own 
profit ;  and  although  in  principle  every  injury  needlessly 
inflicted  on  a  plant  must  in  the  long  run  be  injurious,  it 


38  PLANT   LIFE   ON   THE   FARM. 

may  well  be  and  often  is  the  case  that  the  injury  to  the 
plant  is  compensated  for  by  other  conditions,  and  that, 
in  case  of  difficulties  on  both  sides,  it  is  wisest  to  choose 
the  least  of  two. 

The  Stem  and  its  Work.— As  the  leaves,  whatever 
their  form,  are  nothing  but  outgrowths  from  the  stem, 
and  as  no  leaf  exists  except  it  be  borne  upon  a  stem,  so 
it  would  have  been  more  in  the  natural  order  of  things  if 
mention  had  been  made  of  it  before  the  leaves.  As 
regards  the  nutrition  of  the  plant,  however,  the  stem 
plays  but  a  secondary  part,  as  compared  either  with  the 
root  or  the  leaves,  and  on  this  account  it  may  not  inap- 
propriately be  considered  after  them. 

Botanically,  any  part  of  the  plant  that  produces  leaves, 
or  the  representatives  of  leaves,  is  considered  to  be  stem. 
The  root,  inasmuch  as  it  bears  neither  scales  nor  leaves,  is 
not  stem;  the  "root- stock,"  inasmuch  as  it  does  bear 
scales  and  leaves,  is  truly  a  stem,  even  though  it  may  be 
beneath  ground.  The  long,  creeping  runners  of  "twitch" 
(Triticum  repens)  are  stems,  so  are  the  similar  parts  in 
thistles  and  bear-bind  (Convolvulus  arvensis).  The 
bulbs  of  kohl  rabi  are  clearly  stems,  for  they  bear  leaves, 
or  the  scars  where  leaves  have  once  been.  Beet  roots, 
mangels,  radishes,  turnips,  parsnips,  partake  of  the 
nature  of  roots  and  of  stems  ;  that  is  to  say,  their  lower  ? 
tapering  extremities  are  unquestionably  roots ;  their 
thick  upper  end,  surmounted  by  a  crown  of  leaves,  is  as 
unquestionably  stem.  There  are  anatomical  differences 
— such  as  the  presence  of  a  root-cap,  the  absence  of  sto- 
mata  in  a  root,  and  differences  in  the  mode  of  growth — 
between  roots  and  stems,  but  they  are  not  material  to  our 
present  purpose.  It  will  be  seen,  from  what  has  been 
above  said,  that  the  definition  of  a  stem  (or  of  a  branch, 
which  is  only  a  subdivision  of  a  stem),  as  that  part  of 
the  plant  told  off  to  bear  leaves,  admits  of  very  wide  dif- 


PLANT*  NUTRITION.  39 

ferences  of  form.  We  have  already  alluded  to  some  of 
these  differences,  according  as  the  stem  is  above  or  below 
ground,  covered  with  mere  scale-leaves,  or  bedecked  like 
a  timber  tree  with  true  leaves.  The  pasture  grasses  and 
cereals  have  almost  all  hollow  erect,  knotted  stems  ;  the 
sedges,  which  resemble  the  grasses  so  much,  have  mostly 
angular  unjointed  stems.  The  clovers  have  a  thick  stock 
giving  off  branches  which  trail  along  the  ground.  The 
hop  coils  around  the  supporting  pole  by  means  of  its 
climbing  stem.  Then  there  are  the  differences  in  dura- 
tion associated  with  corresponding  differences  in  texture 
and  internal  construction.  There  are  the  so-called 
annual  stems,  which  would  lie  down,  even  if  they  were 
not  cut  down  after  one  season's  growth ;  there  are  the 
perennial  stems,  like  those  of  fruit  or  timber  trees  or 
shrubs,  and  the  duration  of  whose  existence  may  be 
counted  by  years,  and  often  by  centuries.  Then,  again, 
there  is  an  intermediate  class  of  cases  where  the  root- 
stock  remains  below-ground  for  a  period  long  enough  to 
justify  the  term  perennial,  while  the  branches  or  shoots 
die  down  after  the  seed  is  ripe,  or  are  killed  to  the  ground 
by  a  touch  of  frost,  as  in  the  common  nettles. 

Buds,  Branches,  Tubers,  Etc, — The  branches  or  sub- 
divisions of  a  stem  originate  as  buds  or  "  eyes,"  which 
are  placed  at  the  free  ends  of  the  stem  or  of  its  branches, 
or  which  originate  from  the  side  of  the  stem  or  branch, 
in  what  is  called  the  "axil"  of  a  leaf,  or  of  a  leaf -scale, 
the  axil  being  the  angle  formed  by  the  base  of  the  leaf  at 
the  point  where  it  springs  from  the  stem.  The  traces  of 
their  origin  are  often  lost  as  the  plant  grows,  but  the 
rule  is,  as  it  has  been  stated,  subject  to  a  few  exceptions 
of  no  moment  for  our  present  purpose.  It  is  not  usual 
for  a  bud  to  be  borne  in  the  axil  of  every  leaf,  far  from 
it,  but  this  is  the  place  where  the  side-buds  when  they  do 
exist  are  almost  sure  to  be  found,  The  shoots  which 


40  PLANT  LIFE   ON   THE   FA  KM. 

"tiller"  up  from  the  base  of  the  stems  of  the  wheat 
originate  as  buds  from  the  axils  of  the  lower  leaves,  while 
the  upper  ones  are  destitute  of  them.  When  a  tree  is 
"pollarded,"  a  large  crop  of  buds  makes  its  appearance  ; 
and  the  multiplication  of  some  weeds,  like  thistles  and 
bindweed,  after  their  stocks  have  been  cut  through  with 
the  hoe  at  insufficient  depths  below  the  surface,  is  due  to 
a  like  formation  of  buds. 

The  tuber  of  the  potato  may  be  mentioned  under  this 
heading.  Though  commonly  called  a  root,  because  it 
happens  to  grow  below-ground,  it  is  clearly  a  stem, 
because  it  is  provided  with  "  eyes,"  which  eyes,  as  may 
be  seen  when  the  tuber  begins  to  sprout,  are  nothing  but 
buds.  A  tuber,  then,  is  a  portion  of  the  stem  of  the 
plant,  in  which  the  tissues  become  thickened  and  filled 
with  nutritive  matter  (in  this  case  starch),  which  is  pro- 
vided with  buds,  and  which,  when  once  fully  formed,  is 
separated  from  the  parent  haulm  or  stem  by  the  gradual 
decay  and  death  of  the  latter.  A  tuber  of  this  kind  ful- 
fils in  the  economy  of  the  plant  much  the  same  purpose 
as  the  seed  ;  and  hence  the  term  ( '  seed  potato,"  though 
far  from  correct  in  a  technical  sense,  conveys,  neverthe- 
less, a  not  wholly  incorrect  idea. 

A  "bulb,"  such  as  that  of  an  onion,  is  a  portion  of 
the  stem  modified  for  the  same  purposes  as  the  tuber ; 
but  whereas  in  a  tuber  the  stem  itself  is  swollen,  and  the 
leaves  reduced  to  the  merest  scales,  in  a  bulb  the  condi- 
tions are  reversed  :  the  fleshy  scales  of  an  onion  bulb  are 
really  the  bases  of  the  leaves,  as  any  one  may  see  who 
will  examine  an  onion  in  growth,  while  the  stem  itself  is 
reduced  to  a  mere,  flat,  and  not  very  thick  plate,  from 
the  sides  of  which  emerge  the  leaves.  The  term  balb,  as 
applied  to  such  a  root  as  the  turnip,  is  inaccurate. 

These  illustrations,  taken  from  plants  most  familiar  to 
the  cultivator,  will  suffice  to  show  the  general  character 
of  the  stem  and  its  subdivisions,  and  will  indicate  the 


PLANT  NUTRITION.  41 

great  extent  of  variation  there  is  in  its  outward  charac- 
teristics. The  inward  conformation  of  the  stem  varies 
according  to  the  nature  of  the  plant — its  age  and  the 
purpose  it  fulfils.  The  structure  of  the  stem  of  a  timber 
tree  and  that  of  a  potato  tuber — both,  as  we  have  seen, 
forms  of  stems — are  naturally  different.  In  the  one  case 
thin- walled  cells  filled  with  starch  predominate,  in  the 
other  wood-cells  and  fibres  filled  with  woody  matter  are 
most  abundant.  Still,  great  as  are  the  differences  in  the 
manner  in  which  the  structural  elements  are  arranged  in 
different  cases,  those  elements  are  precisely  the  same  as 
those  mentioned  as  existing  in  the  root  and  in  the  leaf  ; 
and  the  structure  of  a  stem,  however  ultimately  compli- 
cated, is  in  the  first  instance  quite  simple,  being  merely 
an  aggregation  of  cells.  Another  stem,  of  very  different 
general  appearance  it  may  be,  began  in  precisely  the 
same  way.  It  is  only  necessary  here  to  allude  in  passing 
to  the  variations  in  internal  structure,  according  to  cir- 
cumstances, as  they  must  necessarily  be  referred  to  again 
when  dealing  with  the  office  of  the  stem  and  its  mode  of 
growth. 

Ises  of  the  Stem — the  Sap. — Having  gained  a  general 
notion  of  the  nature  and  construction  of  the  stem,  it  is 
necessary  to  enquire  as  to  its  office.  What  does  it  do  for 
the  plant  ?  The  answer  to  this  may  in  a  measure  be 
gleaned  from  what  has  been  said  as  to  the  office  of  the 
leaves.  The  necessity  for  their  exposure  to  sunlight  has 
been  shown,  and  to  ensure  this  exposure,  and  to  provide 
that  one  leaf  shall  overshadow  and  interfere  with  its 
neighbor  as  little  as  possible,  the  stem  lengthens,  and 
the  leaves  are  thrown  off,  now  on  this  side,  now  on  that, 
so  that  each  shall  do  its  own  work  under  the  most  favor- 
able circumstances,  and  hinder  its  neighbor  to  the  least 
possible  degree.  One  leaf  would  not  be  of  much  use, 
but  the  aggregation  of  many  produces  a  timber  tree. 


42  PLA2STT  LIFE   ON   THE   FARM. 

One  leaf's  work  would  probably  not  suffice  to  build  up  a 
grain  of  wheat,  the  aggregation  of  them  serves  to  form  a 
sheaf  of  plump  ears.  The  stem,  in  fact,  is  the  agency 
by  which  the  work  of  individual  leaves  is  combined  and 
concentrated  for  the  general  benefit  of  the  plant.  Each 
separate  leaf,  like  each  separate  cell,  has  a  life  of  its  own, 
and  to  some  extent  is  independent  of  every  other  leaf ; 
but,  if  they  are  to  be  of  any  use  to  the  plant  as  a  whole, 
there  must  be  a  co-operation.  The  stem  and  its  branches 
supply  the  means  for  this  co-operation.  Moreover,  there 
must  also  be  co-operation  between  the  root  and  the  leaves. 
Eoot  action  by  itself  wOuld  not  benefit  the  plant,  even  if 
it  were  practicable.  Leaf  action,  apart  from  the  root, 
would  soon  come  to  an  end.  The  leaves  by  their  copious 
evaporating  surfaces  act  as  suckers  to  draw  up  the  water 
from  the  soil  by  the  agency  of  the  roots.  Thus  as  the 
stem  is  the  agent  between  leaf  and  leaf,  so  it  is  the  go- 
between  betwixt  the  roots  and  the  leaves.  Apart,  then, 
from  its  function  of  bearing  leaves  and  flowers  in  such 
numbers  and  in  such  manner  as  shall  secure  the  greatest 
benefit  to  the  plant  under  the  circumstances  in  which  it 
is  placed — apart  also  from  its  office  of  storing  up  food 
for  future  use — we  have  to  consider  how  it  is  that  the 
stem  acts  as  the  go-between  betwixt  the  root  and  the 
leaves,  and  between  the  leaves  themselves. 

Ascent  of  Liquids. — It  is  certain  that  liquids,  chiefly 
water,  and  gases,  mount  up  from  the  soil  to  the  leaves. 
How  they  enter  the  root  has  been  explained,  and  their 
passage  up  the  stem  against  the  direction  of  gravity  may 
be  accounted  for  on  like  principles  of  diffusion.  There 
are,  however,  various  circumstances  which  aid  the  up- 
ward flow  of  the  liquid.  The  distended  condition  of 
the  cells  and  the  swollen  state  of  their  walls  must  exer- 
cise pressure  on  the  contained  fluids,  the  direction  of 
which  is  mostly  from  below  upwards.  This  pressure,  or 


PLANT  NUTRITION.  43 

squeezing  process,  is  augmented  by  the  swaying  of  the 
branches  or  the  movements  of  the  leaves.  Even  more 
powerful  must  be  the  effect  of  the  atmospheric  pressure 
urging  up  the  liquid  to  fill  the  place  of  that  evaporated 
from  the  leaf  surface.  This  upward  current  is  naturally 
most  active  at  the  period  of  growth,  and  the  channels 
through  which  it  flows  are  necessarily  those  where  the 
conditions  for  osmosis  are  most  propitious.  In  propor- 
tion, therefore,  as  the  cells  become  filled  with  woody  or 
earthy  material  does  the  current  become  less.  As  the 
straw  ripens  or  the  timber  hardens  by  the  formation  of 
wood  in  its  cells,  so  does  the  flow  of  liquid  diminish,  the 
leaves  in  their  turn  and  degree  become  obstructed  and 
fall,  and  the  current,  deprived  of  their  stimulus,  becomes 
feeble. 

But  while  in  thus  alluding  to  some  of  the  duties  of 
the  stem,  we  have  had  to  note  the  existence  during  the 
period  of  growth  of  a  current  of  liquid  whose  general 
direction  is  upward,  it  is  necessary  to  point  oat  that  the 
direction  is  not  exclusively  upward,  but  that  it  is  mani- 
fested in  whatever  direction  the  resistance  is  least  and 
where  growth  may  be  going  on  most  actively  at  the  time. 
Again,  it  is  necessary  to  guard  against  the  still  prevalent 
fallacy  attaching  to  the  use  of  the  word  "  sap."  That 
term  was  first  employed  when  it  was  imagined  that  a 
regular  circulation  of  fluid  took  place  in  plants  from 
root  to  leaf,  and  from  leaf  back  to  root — just  as  in  ani- 
mals the  blood  courses  from  the  heart  through  the  arteries 
to  the  capillaries,  and  back  from  the  capillaries  to  the 
heart  by  the  veins.  In  the  case  of  the  higher  animals 
there  is  a  continuous  series  of  tubes  to  convey  the  fluid, 
and  that  fluid  is  uniformily  arterial  or  venous.  It  is 
quite  otherwise  with  plants  ;  there  is  no  continuous  tube 
or  set  of  tubes,  and  there  is  no  fluid  of  uniformily  the 
same  composition  throughout.  Near  the  root  the  juice 
of  the  plant  has  one  composition,  near  the  leaf  another. 


44  PLANT   LIFE   OK   THE  FARM. 

The  word  "  sap,"  then,  though  convenient,  must  not  be 
used  or  conceived  of  as  indicating  the  existence  of  a  cur- 
rent absolutely  fixed  in  its  direction  or  uniform  in  its 
composition.  In  other  words,  it  has  but  a  remote  analogy 
to  the  blood,  with  which  it  is  so  often  compared.  There  is 
an  upward  current  of  watery  fluid,  well  marked  in  spring, 
there  are  downward  and  cross  currents  varying  in  direc- 
tion and  intensity  according  to  the  requirements  of  the 
growing  tissues  and  their  conformation.  These  have 
only  indirect  connection  with  the  main  upward  flow  just 
referred  to. 


CHAPTER  III. 
GROWTH. 

Growth  and  extension.— Growth  of  cells.— Growing  points.— Growth  of 
roots,  stems,  and  leaves. — Form  as  dependent  on  growth. — Move- 
ments dependent  on  growth. — Movements  of  protoplasm. — Turges- 
cence. — Circumnutation  of  roots,  stems,  leaves. — Seedling  plants. 

In  considering  the  growth  of  plants  we  have  to  distin- 
guish that  growth  which  is  mere  extension  of  old  material 
from  that  which  is  the  result  of  the  formation  of  new 
substance.  We  have  an  illustration  of  the  first  case  in 
the  earliest  stages  of  germination  of  a  seed,  or  in  the 
sprouting  of  a  potato  in  a  cellar.  Growth  may  and  does 
take  place  in  such  instances  without  any  real  increase  of 
substance,  or  any  augmented  weight  save  what  may  be 
derived  from  water.  The  plant  in  this  stage  lives  upon 
the  resources  stored  up  in  its  tissues,  and  will  continue 
to  do  so  until  they  are  exhausted.  But  growth,  in  the 
sense  of  real  increase  of  substance  or  of  increased  weight 
from  the  addition  of  new  material,  depends  upon  the 
amount  of  carbon  assimilated,  as  already  referred  to 
under  the  heading  of  leaves,  A  plant  with  leaf-green  or 


GROWTH."  45 

chlorophyll  in  its  tissues  (and  it  is  with  these  alone  that 
we  are  here  concerned)  gains  carbon  in  the  form  of  car- 
bonic acid  gas  when  it  is  exposed  to  light,  and  loses  it 
constantly,  whether  in  light  or  darkness.  Nevertheless, 
as  the  total  gain  is  greater  than  the  loss,  the  balance  is  in 
favor  of  the  plant.  The  plant  may  thus  be  considered 
to  be  the  result  of  the  greater  amount  of  work  done 
(under  the  influence  of  sunlight)  through  the  medium 
of  the  green  cells  than  of  that  accomplished  by  the  color- 
less cells,  even  though  their  action  is  continuous,  and 
that  of  the  green  cells  intermittent.  It  is  for  us  now  to 
enquire  how  this  increase  of  substance,  how  this  growth 
and  building  up  of  new  materials  takes  place.  The  cir- 
cumstances that  are  propitious,  or  which  are  antagonis- 
tic to  it,  have  been  considered  ;  it  remains  to  enquire 
into  the  way  in  which  the  process  itself  is  effected,  and, 
for  this  purpose,  we  must  revert  to  the  fabric  of  the 
plant,  and  go  back  to  the  cell. 

Growth  of  Cells, — The  perfect  cell,  as  has  been 
explained,  consists  of  a  membranous  bag  enclosing  the 
protoplasm,  some  liquid  contents,  and  in  the  growing 
state  a  small,  highly  refracting  oval  body  known  as  the 
"  nucleus."  The  growth  of  a  cell  may  take  place  in  one 
of  three  different  ways.  There  may  be  simple  extension 
of  the  cell  membrane,  which  becomes  stretched  by  the 
influx  of  fluid  into  its  cavity,  producing  a  state  of  "tur- 
gescence  "  in  the  cell.  But  this  turgescence,  which  is  of 
intermittent  occurrence,  is  of  itself  hardly  to  be  truly 
considered  as  growth  in  the  sense  of  the  formation  of  new 
material,  although  so  closely  associated  with  it  that  no 
true  growth  can  take  place  without  it. 

A  second  mode  of  growth,  resulting  in  the  real  addition 
of  material,  and  consequent  increase  of  weight,  is  that 
called  "  intercalary,"  because  new  material  is  supposed 
to  be  intercalated  or  squeezed  in  between  the  old.  Thus, 


46  PLANT  LIFE  ON  THE  FABM. 

the  molecules  of  cell-membrane  are  separated  by  the  pres- 
sure caused  by  the  turgid  protoplasm,  and  into  the  inter- 
stices so  formed,  new  molecules  of  membrane  formed  by 
the  protoplasm  are,  as  it  were,  squeezed.  The  process  is 
as  if  a  number  of  grains  of  sand  were  laid  upon  a  table, 
each  grain  just  touching  its  neighbor,  and  then  a  new 
grain  were  forced  in  between  two  others,  only  in  this  case 
the  new  grain  is  formed  in  the  cell  itself.  The  requisite 
pressure  is  afforded,  in  the  case  of  the  cell,  by  the  grow- 
ing protoplasm  within,  and  by  the  influx  of  fluid  into 
the  cell  by  osmosis,  producing  a  condition  of  turgescence. 
The  growth  of  the  protoplasm  itself  takes  place  precisely 
in  the  same  way  as  that  of  the  cell  membrane — viz.,  by 
the  formation  of  new  particles,  which  are  squeezed  in  by 
intercalary  growth  between  the  older  ones.  New  matter 
is  also  deposited  on  the  outer  surface  of  the  protoplasm 
or  inner  surface  of  the  cell  wall. 

Lastly,  growth  is  effected,  not  merely  by  extension  of 
old  cells,  or  by  incorporation  of  new  materials  with  old, 
but  by  actual  increase  in  the  number  of  cells.  This 
increase  in  number  has  been  brought  about  by  the  sub- 
division of  the  protoplasm  into  two  or  more  segments, 
each  of  which  becomes  invested  by  cell-membrane. 

For  full  details  as  to  the  various  ways  in  which  division 
of  the  protoplasm  and  the  formation  of  new  cells  take 
place,  reference  must  be  made  to  text  books.  What  has 
been  here  said  is  sufficient  to  indicate  the  general  nature 
of  growth  in  the  organs — with  which  we  are  here  most 
concerned — the  root,  the  stem,  and  the  leaf. 

Growing  Points. — As  has  been  stated,  all  the  parts  of 
plants  are  at  first  wholly  cellular  and  structurally  indis- 
tinguishable ;  but,  as  growth  goes  on,  not  only  their 
outer  form  alters,  but  the  form  and  arrangement  of  their 
constituent  cells  also,  so  that  various  tissues — fibrous, 
woody,  vascular,  or  epidermal — are  formed  ;  and  thus  it 


GROWTH.  47 

comes  about  that  in  the  fully  developed  root  the  internal 
structure  and  the  arrangement  of  the  tissues  are  different 
in  the  great  majority  of  cases  from  those  of  the  stem, 
those  of  the  stem  from  those  of  the  leaf,  and  so  on — dif- 
ferent, that  is  to  say,  in  so  far  as  the  arrangement  of  the 
elementary  cells  and  tissues  go,  rather  than  as  far  as  the 
cells  themselves  and  their  modifications  are  concerned. 
But  while  there  is  this  difference  in  the  structure  of  the 
adult  leaf,  stem,  and  root  respectively,  all  the  time  these 
organs  retain  their  active  faculty  of  growth  there  remains 
a  portion  of  the  cellular  tissue  in  its  original  unmodified 
condition — the  cells  ready  to  divide  and  multiply  and  so 
bring  about  the  growth  of  the  organ.  This  portion  is 
called  the  "  cambium  "or  "  meristem."  So  far  as  growth 
in  length  is  concerned,  there  are  certain  special  points 
where  subdivision  of  cells  is  most  active.  These  are 
called  the  "growing  points."  At  these  places  the  cells 
divide  rapidly,  each  cell  remaining  small,  and  not,  as 
elsewhere,  greatly  extending  its  size  by  interstitial 
growth. 

Growth  of  Roots. — The  growing  point  of  a  root,  so 
far  as  its  length  is  concerned,  is  comprised  within  a 
small  area  just  above  the  extreme  tip,  the  extreme  tip 
itself  being,  as  previously  stated,  covered  by  a  little  cap 
shed  off  from  the  skin  of  the  root  and  serving  as  a  shield 
to  it  in  its  progress  through  the  soil. 

That  the  growth  in  length  takes  place  over  a  very 
small  area  adjacent  to  the  tip  of  the  root  is  proved  by  a 
very  simple  observation.  If  marks  be  made  on  the  grow- 
ing root  at  equal  distances  apart,  say  one-eighth  inch, 
and  the  progress  of  growth  be  watched  from  day  to  day, 
then  it  will  be  found  that  while  the  uppermost  marks 
remain  equi-distant,  those  near  the  tip  become  more  or 
less  widely  separated.  This  experiment  is  easily  carried 
out  with  a  hyacinth  growing  in  a  glass  vase,  or  by  allow- 


48  PLAKT  LIFE   GIST  THE   FAftM. 

ing  a  bean  to  germinate  on  the  surfafce  of  wet  moss.  It 
will  thus  also  be  seen  that  the  actual  area  in  which 
growth  in  length  is  going  on  is  very  small.,  and  that  its 
greatest  activity  is  not  exactly  at  the  extreme  point,  but 
a  little  above  it,  between  it  and  the  point  where  the  root- 
hairs  begin  to  emerge.  There  is,  then,  in  the  growing 
root — first,  at  the  extreme  tip  a  root-cap  or  shield,  con- 
stantly renewed  from  within  by  the  growth  of  the  cells 
above  or  within  it ;  then  a  region  of  very  limited  extent, 
devoted  to  the  growth  in  length  of  the  root ;  and  above 
that  a  portion,  usually  but  not  always,  provided  with 
root-hairs,  and  which  is  especially  told  oif  to  fulfil  the 
duties  of  absorption. 

As  the  upper,  thicker  part  of  the  root  is  relatively 
fixed,  it  will  be  seen  how  the  fine  root  fibrils  are,  by  the 
situation  of  their  growing  point,  enabled  to  push  their 
way,  by  constant  renewal  at  their  growing  point,  in 
amongst  the  particles  of -the  soil  when  the  conditions  are 
favorable. 

Growth  of  the  Stem, — In  the  case  of  the  stem  and 
branches,  the  growing  points,  by  whose  agency  increase 
in  length  takes  place,  are  placed  at  the  summit  of  the 
stem  or  of  its  subdivisions,  the  branches.  The  growing 
points  then  form  the  substance  of  the  "  buds,"  which  are 
either  invested  by  leaf -scales  as  protectors  and  stores  of 
nourishment,  as  in  the  case  of  bulb-scales,  or  by  perfect 
leaves.  The  increase  in  the  thickness  of  stems  takes 
place  also  by  means  of  the  growing  tissue  or  cambium, 
the  situation  of  which  is  different  in  the  two  main  groups 
of  "Exogens"  and  "  Endogens." 

To  the  former  series  belong  all  our  trees  and  shrubs, 
the  clovers,  beet-roots,  turnips,  and  the  vast  majority  of 
plants  which  have  the  veins  of  their  leaves  disposed  in  a 
network.  In  these  plants  the  woody  bundles  of  which 
the  stem  is  principally  made  up  consist  of  "  wood  cells  " 


GROWTH.  49 

and  "  bast  cells/7  with  vessels  of  various  kinds  ;  and  on 
the  outer  side  of  each  bundle  is  a  thin  layer  of  cambium 
tissue  capable  of  growth,  and  in  virtue  of  which  the 
woody  bundles  increase  on  their  outer  surface.  These 
woody  bundles  accumulate  in  wedge-like  masses,  and 
these  again  are  arranged  in  concentric  rings  around  the 
central  cellular  pith,  thus  forming  the  rings  visible  on 
the  cut  surface  of  the  trunk  of  a  tree,  one  such  ring 
generally  indicating,  in  these  latitudes,  the  growth  of 
one  season,  or  at  least  of  one  growing  period. 

In  Endogens,  to  which  all  the  cereals,  and  the  grasses 
and  almost  all  plants  in  which  the  veins  of  the  leaf  run 
parallel  or  nearly  so,  the  woody  bundles  have  their  cam- 
bium tissue  in  the  centre  of  each  bundle,  so  that  their 
growth  in  diameter  is  limited  by  the  pressure  of  the  older 
tissues  outside,  and  there  are  no  concentric  rings  in  the 
stem.  Indeed,  in  this  country,  such  plants  do  not  pro- 
duce a  woody  stem. 

Growth  of  Leaves, — The  growing  points  of  leaves  oc- 
cur in  various  situations,  according  to  the  kind  of  leaf. 
Sometimes  and  more  generally  the  direction  of  principal 
growth  is  from  within  outward — that  is  to  say,  from  the 
centre  outward  (centrifugal)  ;  in  other  cases,  the  general 
tendency  is  in  the  opposite  direction  (centripetal).  In 
addition  to  these  growing  points  at  definite  spots,  where 
new  cells  are  always  forming  during  the  active  period, 
new  growth  may  occur  in  isolated  spots  by  the  formation 
of  growing  cells  in  the  midst  of  or  between  others  that 
have  lost  their  faculty  of  growth,  and  thus  growth  in  the 
substance  of  the  plant  may  take  place  by  intercalation  as 
well  as  at  the  extremities. 

To  repeat,  then,  true  growth  consists  in  the  formation 
of  new  protoplasm  from  the  old,  and  in  the  division  of 
the  protoplasm  into  new  cells.  This  division  takes  place 
especially  and  primarily,  so  far  as  growth  in  length  is 


50  PLANT  LIFE   OK  THE  FAKM. 

concerned,  at  certain  definite  places  called  growing  points. 
The  new  tissues  thus  formed  are  at  first  wholly  cellular, 
some  of  the  constituent  cells  retaining  the  faculty  of  sub- 
division, though  sometimes  not  manifesting  it  till  a  later 
period  ;  while  others  become  modified  in  various  ways  as 
growth  goes  on,  forming  wood-cells,  fibres,  epidermis,  and 
so  on. 

Form  as  Dependent  on  Growth, — If  we  could  sup- 
pose the  degree  or  intensity  of  growth  to  be  equal  on  all 
sides,  and  without  impediment  or  obstacle,  the  result 
would  be  a  spherical  plant ;  and  such  plants  do  exist, 
but,  in  the  great  majority  of  cases,  the  conditions  are 
such  that  growth  is  greater  in  amount  in  one  direction 
than  in  another ;  or  it  may  be  that  while  pait  remains 
stationary  another  part  grows,  the  result  being  a  change 
of  form.  In  the  case  of  the  main  root  and  stem,  the 
principal  direction  of  growth  is  vertically  upwards  and 
downwards  ;  in  the  case  of  leaves,  the  main  direction  of 
growth  is  horizontal,  so  that  while  a  stem  or  a  root  may 
be  divided  from  above  downwards  into  two  nearly  equal 
halves,  one  half  the  reflex  of  the  other,  a  leaf  must  be 
divided  horizontally,  and  the  upper  surface  and  the  lower 
surface  are  commonly  different.  Variations  in  form  are 
dependent  not  only  on  variations  in  the  direction  of 
growth,  but  upon  the  place  where  growth  is  taking  place, 
and  whether  it  be  limited,  as  in  the  case  of  the  growing 
points  and  cambium  tissue  already  referred  to,  or  general 
throughout  the  mass. 

The  form  of  the  plant  or  of  any  particular  part  of  it 
will  also  of  necessity  vary  according  as  the  growth  is  con- 
tinuous or  intermittent,  equal  or  unequal.  These  are  all 
circumstances  readily  understood,  and  they  are  referred 
to  here  because  they  furnish  the  reasons  for  the  develop- 
ment of  bulb  and  root,  as  of  turnip  and  mangel  as  con- 
trasted with  that  of  foliage.  In  them  also  must  be 


GEOWTH.  51 

sought  the  explanation  of  thin  ears  of  wheat  or  defective 
hay  crops. 

Phenomena  associated  with  Growth  and  Activity.— 

Under  this  heading  may  be  mentioned  the  various  move- 
ments in  the  liquid  (cell-sap),  contained  within  the  cells, 
and  in  the  protoplasm,  which  are  observed  in  living  cells, 
especially  in  those  in  which  the  vital  processes  are  most 
active.  Here  also  may  be  mentioned  the  movements 
associated  more  or  less  directly  with  growth,  and  the 
influence  of  various  agencies,  such  as  of  gravitation, 
light,  temperature,  etc.,  on  plants  and  their  several 
organs.  These  phenomena  and  these  influences  are  more 
manifest  during  active  growth  ;  and  when  they  occur  in 
living  organs  which  have  ceased  their  actual  growth, 
they  do  not  essentially  differ,  though  they  may  do  so  in 
degree,  and  may  also,  to  some  extent,  be  modified  in 
character. 

Movements  as  Dependent   on   Growth,— But  a  few 

years  ago  the  notion  of  movement  taking  place  in  plants, 
other  than  that  produced  by  the  wind  or  other  mechani- 
cal agency,  was,  if  not  entirely  ignored,  so  little  con- 
sidered that  the  immobility  of  plants  was  contrasted  with 
the  mobility  of  animals.  We  know  now  that  even  loco- 
motion is  by  no  means  an  exclusive  attribute  of  animals, 
but  for  our  present  purposes  we  need  only  refer  to  those 
movements  more  immediately  connected  with  the  growth. 

Movement  of  Protoplasm. — The  protoplasm  is  a  very 
mobile  substance,  and  the  cell-membrane  is  very  elastic, 
while  both,  as  has  been  shown,  are  permeable  in  various 
degrees  by  water,  the  consequence  of  which  is  that  under 
favorable  conditions  the  cells  become  turgid.  As  the 
degree  of  turgescence  varies  according  to  circumstances, 
tension  being  followed  by  flaccidity,  and  flaccidity  over- 


52  t>LAKT  LIFE   OK  THE   FAKM. 

come  by,turgidity,  is  of  course  obvious  not  only  that 
changes  of  form  must  ensue  from  these  differences  in  the 
degree  of  tension  of  the  cells,  but  that  movements  of  the 
parts  concerned  must  also  take  place.  These  movements 
are,  of  course,  more  obvious  when  growth  is  irregular 
and  unequal.  Turgescence  of  the  cells,  as  has  been  said, 
is  an  essential  condition  of  growth,  and  if  this  turges- 
cence  take  place  on  one  side  of  a  stem,  or  on  one  surface 
of  a  leaf  only,  a  curve  will  be  produced,  the  convexity  of 
which  will  be  along  the  line  of  greatest  swelling  and 
growth — the  concavity  on  the  opposite  side  where  growth 
is  less  active,  or  altogether  inoperative.  The  rapidly 
growing  upper  surface  will  be  restrained  as  by  a  bridle 
by  that  part  which  is  growing  more  slowly  or  not  at  all, 
and  hence  the  curvature. 

Circumnutation. — Now,  let  us  suppose  the  very  fre- 
quent case  where  the  greatest  intensity  of  growth  is  now 
in  one  place,  now  in  another,  then,  of  course,  we  should 
have  the  curvatures  first  in  one  place,  and  then  in 
another,  and  this  is  what  happens  in  the  case  of  growing 
shoots  whose  tips  gradually  revolve,  forming  circuits  or 
ellipses  of  greater  or  less  extent  with  greater  or  less 
rapidity,  according  to  circumstances.  This  movement, 
which  is  not  usually  perceptible  except  by  the  use  of 
delicate  instruments,  may  sometimes  be  watched  by  the 
naked  eye,  even  in  the  case  of  such  apparently  stiff  parts 
as  the  leading  shoots  of  Firs.  Among  other  objects 
gained  by  this  movement  of  ' '  revolving  nutation,"  or  as 
Darwin  called  it,  (<  circumnutation,"  is  the  exposure  of 
each  leaf  in  turn  to  the  conditions  of  light  most  favor- 
able to  it. 

Movement  of  the  Tip  of  the  Root, — While  the  elon- 
gation of  the  root  near  the  tip  takes  place  in  the  manner 
described,  the  force  of  growth  is  not  equal  throughout 


GROWTH.  53 

the  whole  region  at  the  same  time.  Supposing  the  fibril 
to  be  made  up  of  cells  piled  up  one  upon  another  in  lon- 
gitudinal rows,  then  the  greatest  energy  of  growth, 
marked  by  the  turgescence  of  the  cells,  occurs  at  one  time 
in  one  row,  to  shift  at  another  time  into  the  next  row, 
and  so  on  in  succession  all  round  the  root.  The  effect  of 
this  greater  turgescence  and  intensity  of  growth — now  in 
one  place,  now  at  another — is  to  move  the  tip  of  the  root, 
not"  in  a  circle,  because  growth  is  going  on  behind  the 
tip  as  it  moves,  but  in  an  advancing  spiral  coil,  so  that 
the  tip  is  forced  to  enter  the  soil  and  to  penetrate 
between  its  particles,  just  as  the  point  of  a  corkscrew  is 
made  by  the  pressure  of  the  hand  to  penetrate  the  cork, 
the  pressure  of  the  hand  being  replaced,  in  the  case  of 
the  root,  by  the  superincumbent  weight  of  soil. 

Darwin,  who  has  done  so  much  to  illustrate  and  make 
known  the  movements  of  roots  and  of  other  organs,  cal- 
culates that  the  terminal  growing  part  of  the  radicle  (or 
primary  root  produced  from  the  seedling  plant)  "in- 
creases in  length  with  a  force  equal  to  ...  the  pressure 
of  at  least  a  quarter  of  a  pound — probably  with  a  much 
greater  force  when  prevented  from  bending  to  any  side 
by  the  surrounding  earth.  While  thus  increasing  in 
length,  it  increases  in  thickness,  pushing  away  the  damp 
earth  on  all  sides  with  a  force  of  above  eight  pounds  in 
one  case,  of  three  pounds  in  another  case.  .  .  .  The 
growing  part,  therefore,  does  not  act  like  a  nail  when 
hammered  into  a  board,  but  more  like  a  wedge  of  wood, 
which,  whilst  slowly  driven  into  a  crevice,  continually 
expands  at  the  same  time  by  the  absorption  of  water ; 
and  a  wedge  thus  acting  will  split  even  a  mass  of  rock." 

Movement  of  Stems. — The  circumnutation  of  stems  as 
a  result,  or  at  least  as  a  concomitant  of  active  growth,  is 
most  easily  seen  in  the  case  of  climbing  plants  like  the 
hop,  the  free  ends  of  whose  growing  shoots  sweep  round 


54  PLANT  LIFE   ON  THE   FARM. 

in  wide  cttrves  till  they  come  in  contact  with  a  support 
round  which  to  twine,*  and  thus  remove  their  leaves 
from  the  surface,  where  they  would  be  overshadowed,  to 
a  point  of  vantage  where  they  would  be  exposed  to  light, 
and  this  with  the  least  expenditure  of  material.  Very 
similar  are  the  movements  executed  by  stolons  and  run- 
ners, as  of  the  strawberry,  and  probably,  though  the 
cases  have  not  been  studied,  of  the  trailing  rhizomes  of 
the  twitch  (Triticum  repens),  the  scions  of  the  meadow 
poa  (Poa  pratensis),  of  the  clovers,  of  the  milfoil,  etc. 
Such  a  movement  would  facilitate  the  introduction  of 
these  runners  between  other  plants,  and  thus  secure  the 
extension  of  their  area  of  growth.  The  movements  in 
the  stem  are  more  especially  connected  with  growth  ; 
they  cease,  or  become  much  enfeebled  after  growth  is  com- 
pleted or  arrested.  Under  certain  circumstances,  however, 
the  faculty  of  growth  is  retained  in  certain  spots  after  it 
has  ceased  elsewhere,  or  if  actual  growth  do  not  take 
place,  yet  some  of  the  phenomena  connected  with  it  may 
occur.  Thus  the  stems  of  grasses,  such  as  of  wheat,  are 
provided  with  thick  "nodes"  or  joints  at  the  places 
whence  the  leaves  spring  from  the  stem.  When  the 
wheat  gets  beaten  down  or  laid  by  a  storm  of  rain  and 
wind,  the  resumption  of  the  erect  position  is  effected  by 
the  medium  of  the  nodes,  which  grow,  or  at  least  become 
turgescent,  especially  on  the  under  surface,  which  thus 
becomes  convex,  while  the  upper  surface,  which  does  not 
grow,  or  at  least  not  to  the  same  extent,  becomes  con- 
cave ;  the  consequence  is  that  the  upper  end  of  the  stem 
becomes  raised — as  may  be  illustrated  thus  : — Let- 
represent  the  joint  of  the  laid  stem  ;  then,  by  the  agencies 
just  mentioned,  the  straight  horizontal  position  is  replaced 

by  the  ascending  one     ,  and  ultimately  by  the  vertical  one 

*See  Darwin,    The  Movements  and  Habits  of  Climbing  Plants, 


GROWTH.  55 

Darwin  has  shown  that  the  joints  of  grass  stems  continue 
to  exhibit  movements  on  a  small  scale  for  a  long  period. 
Supposing  the  stem  to  be  "laid,"  such  movements  would 
clearly  aid  the  upward  tendency  above  described,  and 
facilitate  the  uprising  of  the  stem.  (Darwin,  Power  of 
Movement,  p.  503). 

MoTements  of  Leaves,— The  leaves  of  plants  exhibit 
several  kinds  of  motion  ;  some  periodic,  as  in  the  case  of 
the  so-called  sleep  of  leaves,  some  due  to  the  stimulus  of 
light  or  its  removal,  some  the  consequence  of  contact,  as 
in  the  case  of  the  sensitive  plant;  but  those  to  which 
mention  is  here  made  are  the  result  of  the  same  causes  as 
those  before  alluded  to  in  the  case  of  stems  and  roots. 
The  growth  movements  of  leaves  are  observable  in  the 
stalk,  or  in  the  blade,  or  in  both,  and  are  chiefly  exerted 
in  a  vertical  direction,  so  that  the  leaf  rises  or  falls  ;  but 
as  the  ascent  is  never  quite  in  fche  same  line  as  the  de- 
scent, some  side  to  side  motion  must  also  take  place.  It 
is  noticed  that  the  rise  occurs  generally  in  the  evening, 
the  fall  on  the  following  morning.  These  movements 
are  probably  due  to  the  intensity  of  growth  being  greater 
first  on  one  side,  then  on  the  other. 

Growth-movements  of  the  kind  indicated  have  now 
been  shown  to  exist  in  the  roots,  in  the  stems,  and  in  the 
leaves.  The  probability  is  that  they  occur  more  or  less 
wherever  growth  is  going  on  actively.  In  accordance 
with  this,  it  maybe  mentioned  that  seedling  plants  mani- 
fest these  movements  to  a  remarkable  degree.  Thus-  all 
the  parts  of  seedling  cabbages,  the  radicle,  the  caulicle 
above  the  radicle  supporting  the  seed  leaves  or  cotyle- 
dons, as  well  as  these  latter  organs,  were  observed  by 
Darwin  to  exhibit  growth  movements  facilitating  the 
downward  passage  of  the  root  and  the  upward  progress 
of  the  cauliclesf 


56  PLAixT  LIFE   Otf   THE   FARM. 

CHAPTER  IV. 

SENSITIVENESS. 

Movements  dependent  on  external  conditions.  —  Gravitation,  light, 
heat,  moisture. — Action  of  gravity  on  roots. — Geotropism. — Influ- 
ence of  light,  heat,  moisture,  and  contact  on  roots.— Passage  of 
roots  through  the  soil. — Action  of  gravitation  on  leaves. — Helio- 
tropism. — Sleep  of  leaves. — Action  of  heat  and  moisture  on  leaves. 
— Defensive  arrangements. — Selection  of  hardy  varieties. — Influence 
of  contact  on  leaves. — Action  of  gravity,  light,  heat,  moisture,  and 
contact  on  stems.  —  After-effects.  —  Climbing  plants. —  Combined 
effect  of  external  and  internal  agencies. 

Closely  analogous  to  the  growth-movements  are  a  series 
of  alterations  of  position  dependent  upon  various  circum- 
stances, such  as  gravity,  the  influence  of  heat  and  light 
or  their  absence,  the  result  of  contact  or  irritation,  and 
so  on.  They  are  probably  essentially  of  the  same  nature 
as  the  growth  movements,  but,  unlike  them,  they  are 
not  confined  to  structures  still  in  a  growing  state  •  more- 
over, in  some  cases  they  exhibit  a  sort  of  reflex  action, 
contact  or  irritation  of  one  part  bringing  about  a  move- 
ment of  some  other  part  at  a  distance.  It  is  often  diffi- 
cult to  dissociate  the  effects  of  these  several  movements  ; 
for  a  living  plant  and  its  parts  are  subjected  at  the  same 
time  to  the  combined  influence  of  several  of  these 
agencies,  and  the  force  and  direction  of  growth  are  neces- 
sarily essentially  modified  by  them. 

It  may  be  well  in  this  place  to  indicate  very  generally 
in  what  manner  roots,  stems,  and  leaves  are  sensitive  to 
the  effects  of  gravity,  light,  moisture,  and  actual  contact 
or  irritation,  and  then  to  specify  equally  briefly  what  is 
the  general  character  of  the  results  produced  by  these 
several  causes  acting  singly,  or  in  combination. 

The  Action  of  Gravity  on  Roots. — Oeotropism, — The 

downward  tendency  of  the  main  root  is  one  of  its  most 


SENSITIVENESS.  57 

marked  characteristics,  and  this  tendency  to  grow,  or 
move  towards  the  centre  of  the  earth  under  the  influ- 
ence of  gravitation,  is  known  as  "geotropism,"  the  op- 
posite tendency  being  called  f<  apogeotropism."  Knight 
was  the  first  to  show  that  downward  tendencies  of  the 
root  were  due  to  gravitation,  and  this  he  did  by  causing 
seedlings  to  grow  on  a  wheel  kept  in  motion.  The  effect 
of  gravity  was  here  overcome  by  the  movement  of  the 
wheel,  and  the  rootlets,  instead  of  growing  downwards, 
were  now  directed  away  from  the  centre  of  the  wheel. 
Darwin  shows  (1.  c.,  p.  540)  that  it  is  the  tip  of  the  root 
alone  that  is  involved  in  this  downward  tendency,  the 
destruction  of  the  tip  putting  a  stop  to  the  movement. 
While  the  primary  root  or  radicle  under  favorable  cir- 
cumstances penetrates  the  soil  perpendicularly  downwards, 
the  secondary  ones  bend  obliquely,  not  perpendicularly, 
downwards,  the  tertiary  ramifications  and  their  subdi- 
visions being  so  little  affected  by  geotropism  that  they 
grow  out  freely  in  all  directions.  From  this  manner  of 
growth  in  the  main  root  and  its  branches  respectively,  it 
is  evident  how  the  whole  mass  of  soil  within  their  reach 
becomes,  under  favorable  conditions,  a  happy  hunting 
ground  for  the  roots.  Moreover,  it  has  been  shown  that 
where  the  primary  radicle,  the  origin  of  the  "  tap"  root, 
has  been  destroyed — as  it  often  must  be  in  nature,  by 
insects  or  other  means — the  secondary  roots,  instead  of 
retaining  their  oblique  direction,  assume  that  previously 
taken  by  the  injured  root  and  pass  downwards. 

The  Action  of  Lteht  and  Heat  on  Roots,— The  direct 
action  of  light  upon  ordinary  roots  is,  of  course,  usually 
of  a  negative  character.  The  form  and  direction  of 
growth  in  the  root  may,  however,  be  affected  by  differ- 
ences of  temperature,  experienced  now  on  one  side,  now 
on  another.  Darwin  has  shown  that  the  movements  of 
roots,  due  to  irritation  or  contact,  are  checked  by  too 


58  PLANT   LIFE   ON    THE   FARM. 

high  or  too  low  a  temperature.  During  their  passage 
through  the  soil,  the  roots  must  be  constantly  subjected 
to  variations  of  temperature,  first  on  one  side  and  then 
on  another,  these  variations  giving  rise  to  some  of  the 
curvatures  and  bends  of  the  rootlets.  The  effect  of  an 
excessive  amount  of  heat  in  the  soil  upon  the  germination 
of  seedlings  has  been  studied  by  M.  Prillieux,  and  is  of 
interest  as  indicating  the  conditions  under  which  tuberous 
roots  and  root  stocks  may,  under  certain  circumstances, 
be  formed.  When  seedlings  of  French  beans  and  vege- 
table marrows  were  grown  in  an  overheated  soil,  the 
caulicle  or  portion  of  the  stem  above  the  root  and  between 
it  and  the  seed-leaves  became  preternaturally  swollen 
and  tuberous,  while  growth  in  hight  was  arrested.  The 
increased  development  arising  from  the  heated  soil  took 
place,  therefore,  in  the  very  same  organs  which  constitute 
the  so-called  "  bulbs  "of  turnips  or  "  roots  "  of  swedes 
or  mangels.  The  increased  volume  is  due  principally  to 
an  excessive  development  of  existing  cells  rather  than  to 
a  multiplication  of  new  ones. 

The  Action  of  Moisture  on  Roots. — Much  more 
obvious  to  the  general  observer  is  the  action  of  moisture 
on  roots.  The  distance  to  which  roots  will  travel  in 
search  as  it  were  of  water,  and  the  way  in  which  luxuri- 
ant growth  and  intricate  ramification  are  promoted,  when 
access  to  it  is  obtained,  are  familiar  facts.  Too  frequently 
drain  pipes  get  choked  with  a  mass  of  roots  whose 
structure  has  been  changed,  and  whose  excessive  growth 
has  been  stimulated  by  the  presence  of  copious  supplies 
of  moisture.  If  there  is  an  equal  supply  of  water  all 
round,  the  growth  of  the  roots  will  be  uniform  ;  but  if, 
as  is  more  often  the  case,  there  is  more  water  on  one  side 
than  on  the  other,  then  the  root  will  curve  to  the  side 
where  there  is  the  fullest  supply,  and  the  power  thus 
exerted  to  get  at  the  water  is  greater  than  that  of  gravity. 


SENSITIVENESS.  59 

When  the  tip  of  the  root  is  covered  with  grease,  the  root 
does  not  bend  to  the  wet  surface,  on  which  account  Mr. 
Darwin  and  his  sou  infer  that  sensitiveness  to  moisture 
resides  specially  in  the  tip.  The  relation  these  move- 
ments and  this  growth  bear  to  the  processes  of  nutrition 
carried  on  by  the  roots  is  too  obvious  to  need  further 
comment. 

The  Influence  of  Contact  on  Roots. — The  effect  of 
pressure  such  as  that  caused  by  the  contact  of  any  sub- 
stance, even  if  it  be  very  slight,  is  to  produce  movements 
of  curvature  in  the  root,  the  direction  of  the  curvature 
varying  according  to  the  part  of  the  root  touched.  Thus, 
if  the  root  be  touched  in  the  region  where  growth  is 
going  on  most  actively,  the  root  becomes  concave  on  the 
side  which  is  touched,  convex  on  the  opposite  side,  prob- 
ably because  growth  is  arrested  by  the  pressure  on  the 
one  side,  while  it  is  unrestricted  on  the  other.  The  con- 
sequence of  this  is  that  the  roots  in  such  case  turn 
towards  the  obstructing  substance,  and,  if  it  be  of  small 
dimensions,  coil  themselves  around  it,  or,  if  it  be  too 
large  for  this  purpose,  creep  over  its  surface. 

On  the  other  hand,  if  the  extreme  tip  of  the  root  be 
touched,  the  root  bends  away  from  the  obstruction, 
becoming  convex  on  the  side  where  contact  is  effected, 
concave  on  the  opposite  side,  the  root  sometimes  making 
complete  loops  by  its  continued  curved  growth.  The 
object  of  this  sensibility  to  contact  appears  to  be  to 
enable  the  roots  to  overcome  the  obstacles  they  meet  with 
in  the  soil.  Thus  "  when  a  root  meets  with  an  obstacle 
in  its  way,  the  pressure  on  one  side  of  the  tip  causes  the 
growing  part  of  the  root  to  grow  more  rapidly  on  the  side 
of  the  obstacle,  and  thus  curve  away  from  it "  (F.  Dar- 
win). 

It  will  be  seen  that  the  irritation  from  the  various 
causes  above  mentioned  is  not  merely  local  in  its  effect. 


60  PLANT   LIFE   ON   THE   FARM. 

but  that  it  induces  movement  in  adjoining  parts,  on 
which  account  the  parts  so  influenced  are  spoken  of  as 
"sensitive." 

Passage  of  Roots  through  the  Soil— Summary.— The 

course  followed  by  a  root  through  the  soil  is,  says  Dar- 
win, "  brought  about  and  modified  by  extraordinarily 
complex  and  diversified  agencies — by  geotropism,  acting, 
as  has  just  been  explained,  in  a  different  manner  on  the 
primary,  secondary,  and  tertiary  radicles ;  by  sensitive- 
ness to  contact,  different  in  kind  in  the  apex  and  in  the 
part  immediately  above  the  apex  ;  and  apparently  by 
sensitiveness  to  the  varying  dampness  of  different  parts 
of  the  soil.  .  .  .  The  direction  which  the  apex  takes  at 
each  successive  period  of  the  growth  of  a  root  ultimately 
determines  its  whole  course  ;  it  is,  therefore,  highly  im- 
portant that  the  apex  should  pursue  from  the  first  the 
most  advantageous  direction  ;  and  we  can  thus  under- 
stand why  sensitiveness  to  gravitation,  to  contact,  and  to 
moisture,  all  reside  in  the  tip,  and  why  the  tip  determines 
the  upper  growing  part  to  bend  either  to  or  from  the 
exciting  cause.  A  radicle  may  be  compared  with  a  bur- 
rowing animal,  such  as  a  mole,  which  wishes  to  penetrate 
perpendicularly  down  into  the  ground.  By  continually 
moving  his  head  from  side  to  side,  or  circumnutating,  he 
feels  any  stone  or  other  obstacle,  as  well  as  any  difference 
in  the  hardness  of  the  soil,  and  he  will  turn  from  that 
side.  If  the  earth  is  damper  on  one  than  on  the  other 
side,  he  will  turn  thither  as  to  better  hunting  ground. 
Nevertheless,  after  each  interruption,  guided  by  the 
sense  of  gravity,  he  will  be  able  to  recover  his  downward 
course  and  to  burrow  to  a  greater  depth." 

Elsewhere  Darwin  sums  up  the  root  movements  as  fol- 
lows : — "  We  believe  that  there  is  no  structure  in  plants 
more  wonderful,  so  far  as  its  functions  are  concerned, 
than  the  tip  of  the  radicle.  If  the  tip  be  lightly  pressed, 


SENSITIVENESS.  61 

or  burnt  or  cut,  it  transmits  an  influence  to  the  upper 
adjoining  part,  causing  it  to  bend  away  from  the  affected 
side  ;  and,  what  is  more  surprising,  the  tip  can  distin- 
guish between  a  slightly  harder  and  softer  object  by 
which  it  is  simultaneously  pressed  on  opposite  sides.  If, 
however,  the  radicle  is  pressed  by  a  similar  object  above 
the  tip,  the  pressed  part  does  not  transmit  any  influence 
to  the  more  distant  parts,  but  bends  abruptly  towards  the 
object.  If  the  tip  perceives  the  air  to  be  moister  on  one 
side  than  on  the  other,  it  likewise  transmits  an  influence 
to  the  upper  adjoining  part,  which  bends  towards  the 
source  of  moisture.  When  the  tip  is  excited  by  light, 
the  adjoining  part  bends  from  the  light ;  but  when 
excited  by  gravitation,  the  same  part  tends  towards  the 
centre  of  gravity.  In  almost  every  case  we  can  clearly 
perceive  the  final  purpose  or  advantage  of  the  several 
movements.  Two  or  perhaps  more  of  the  exciting  causes 
often  act  simultaneously  on  the  tip,  and  one  conquers 
the  other,  no  doubt,  in  accordance  with  its  importance 
for  the  life  of  the  plant.  The  course  pursued  by  the 
radicle  in  penetrating  the  ground  must  be  determined  by 
the  tip  ;  hence  it  has  acquired  such  diverse  kinds  of  sen- 
sitiveness. .It  is  hardly  an  exaggeration  to  say  that  the 
tip  of  the  radicle  thus  endowed,  and  having  the  power  of 
directing  the  movements  of  the  adjoining  parts,  acts  like 
the  brain  of  one  of  the  lower  animals,  the  brain  being 
seated  within  the  anterior  end  of  the  body,  receiving  im- 
pressions from  the  sense-organs,  and  directing  the  several 
movements." 

Practical  Inferences. — It  will  be  obvious,  then,  from 
what  has  been  before  said,  that  for  cultural  purposes, 
such  as  the  various  operations  connected  with  tillage,  the 
nature,  quantity,  and  time  of  application  of  manure,  and 
the  like,  the  character  of  root-action  in  general  must  be 
studied  in  connection  with  the  nature  and  properties  of 


62  PLANT   LIFE    ON   THE   FAIIM. 

the  soil.  The  special  form  and  characteristics  of  the 
root  in  the  particular  crop  it  is  wished  to  cultivate — tap- 
rooted,  fibrous-rooted,  fleshy,  surface-rooting,  or  deep- 
rooting,  etc. — must  also  be  taken  into  consideration  in 
the  same  relation. 

Action  of  Gravitation  on  Leaves. — The  tendency  of 
leaves  during  their  growing  period  so  to  place  themselves 
that  their  upper  surface  looks  to  the  heaven,  their  lower 
to  the  earth,  is  a  matter  of  every-day  observation. 
Scarcely  less  familiar  are  the  turns  and  twists  which  the 
leaves  or  their  stalks  make  to  right  themselves  when  by 
any  means  their  normal  position  is  interfered  with.  At 
first  sight  it  would  seem  that  these  movements  must  be 
due  rather  to  the  influence  of  light  than  of  gravitation  ; 
but  as  they  take  place  in  darkness  as  well  as  in  light,  and 
as  they  do  not  take  place  when  plants  are  so  grown  as  to 
be  exempt  from  the  influence  of  gravitation,  it  is  clear 
what  the  true  cause  of  these  movements  is  (Van  Tieghem). 

Action  of  Light  on  Leaves  —  Heliotropism,—  The 

chemical  changes  which  result  from  the  exposure  of  the 
leaves  to  light  have  already  been  alluded  to  under  the 
head  of  nutrition.  It  remains  here  to  mention  the  power 
that  they  have  of  turning  to  the  light,  now  called  '•'helio- 
tropism," and  especially  of  so  placing  their  upper  surface 
as  that  it  shall  form  a  right  angle  to  the  direction  of  the 
light.  It  had  been  surmised  that  the  horizontal  position 
of  leaves,  and  especially  the  position  with  regard  to  the 
direction  of  light,  was  due  to  the  conjoint  action  of 
gravitation  of  geotropism,  of  heliotropism,  and  of  the 
greater  relative  force  of  growth  on  one  or  the  other  sur- 
face. The  particular  direction  assumed  by  the  leaves 
was  supposed  to  be  due  to  the  balance  between  these 
forces  ;  but  by  means  of  experiments  made  with  a  view 
of  annulling  or  counteracting  the  effects  of  gravitation, 


SENSITIVENESS.  63 

and  of  unequal  growth,  Mr.  Francis  Darwin  has  shown 
that  the  power  which  leaves  have  of  placing  themselves 
at  right  angles  to  incident  light  is  due  to  a  special  sensi- 
tiveness. This  sensitiveness  is  capable  of  regulating  the 
action  of  other  forces,  whether  external  to  the  plant,  as 
that  of  gravitation,  or  internal,  such  as  that  controlling 
the  direction  and  amount  of  growth.  The  movements 
of  the  leaves  towards  the  light  are  different  from  others 
which  are  of  a  periodic  character,  in  that  they  are  influ- 
enced hy  the  direction  rather  than  by  the  intensity  of 
the  light. 

The  growth  of  leaves,  like  growth  in  general,  is  re- 
tarded by  the  action  of  light.  Growth,  therefore,  is 
carried  on  independently  of  and  not  contemporaneously 
with  nutrition  by  the  leaf,  so  far  as  the  latter  consists  in 
the  decomposition  of  carbonic  acid  and  the  fixation  of 
the  carbon.  Thus  it  has  been  shown  hy  Dr.  Vines  that 
leaves  will  grow  in  darkness,  or  under  the  influence  of 
blue  light ;  in  air  deprived  of  carbonic  acid ;  and  even  in 
the  absence  of  chlorophyll.  But  although  there  is  thus 
shown  to  be  no  direct  relation  between  nutrition  and 
growth,  yet  there  is,  of  course,  an  indirect  relation ; 
growth  under  the  apparently  adverse  conditions  just 
mentioned,  being  only  possible  in  cases  where  there  is 
available  some  store  of  nourishment  previously  formed  by 
assimilation. 

Sleep  of  Leaves. — Other  movements  of  leaves  are  de- 
pendent chiefly  on  the  amount  of  light  to  which  they  are 
subjected.  Of  such  nature  are  the  movements  popularly 
supposed  to  be  connected  with  the  sleep  of  plants,  but 
which  have  no  real  analogy  with  the  sleep  of  animals. 
Clover  and  sainfoin  leaves  show  these  nocturnal  move- 
ments very  clearly,  the  leaflets  folding  up  at  the  approach 
of  night,  and  unfolding  in  the  morning  as  the  light  in- 
creases. Plants  exposed  to  the  dark  end  of  the  solar 


G-i  PLANT   LIFE   ON  THE   FAKM.- 

spectrum  manifest  similar  movements.  Some  leaves  are 
raised,  others  depressed,  some  fold  upwards,  some  down- 
wards, but  the  object  in  all  cases  is  probably  the  same — 
namely,  to  shield  the  leaves  from  the  cooling  effect  of 
radiation  from  the  surface  during  the  night,  a  process 
which  produces  the  same  effects  as  actual  frost  would  do. 
The  cause  of  these  movements  is  due  to  a  swelling  or 
turgescence  and  a  consequent  growth  first  on  one  side 
and  then  on  another  side. 

Action  of  Heat  and  Moisture  upon  Leaves,  — But 
little  beyond  what  has  already  been  mentioned  need  be 
said  upon  the  relation  of  heat  and  moisture  to  leaves.  A 
few  words  upon  the  influence  of  excessive  temperatures 
may,  however,  here  be  appropriately  given. 

If  the  temperature  fall  below  a  given  point,  variable 
for  each  species,  and  also  for  each  individual  plant,  the 
functions  of  the  leaf  are  held  in  abeyance,  chlorophyll  is 
only  imperfectly  formed  (hence  the  yellow  tinge  of 
frosted  wheat) ;  and  if  the  temperature  be  still  further 
depressed  death  results. 

Action  of  Frost, — When  a  leaf  is  frozen  the  fluid  con- 
tents escape  from  the  cells  by  permeation  through  their 
membrane,  and  freeze  on  the  outside  of  the  cell,  so  that 
the  spaces  between  them  are  full  of  ice.  It  rarely  hap- 
pens that  the  juices  of  the  cells  freeze  in  the  interior  of 
the  cells — if  they  do,  rupture  of  the  cell  wall  and  death 
are  the  most  probable  results.  Under  ordinary  circum- 
stances the  cells  lose  that  turgescence  which,  as  has  been 
stated,  is  necessary  for  their  activity.  All  the  functions 
of  life  are  arrested,  not  necessarily  never  to  be  resumed, 
for,  in  some  cases,  when  the  ice  in  the  tissues  of  the 
plant  melts,  the  water  is  re-absorbed  by  the  membrane, 
and  life  action  is  resumed.  Winter  wheat  must  fre- 
quently become  frozen  in  this  manner,  but  it  is  com- 


SENSITIVENESS.  05 

paratively  rarely  that  the  plant  is  killed  outright,  farmers 
wisely  choosing  those  varieties  which  experience  has 
shown  to  be  the  hardiest.  If  the  cold  is  sufficient  to  kill 
the  leaves  or  any  portion  of  them,  the  leaves  become  limp 
and  blackened.  The  limpness  is  easily  accounted  for  by 
the  causes  we  have  mentioned,,  as  well  as  by  the  stoppage 
of  supplies  of  water  from  the  root.  The  discoloration  is 
the  effect  of  some  molecular  change  in  the  chlorophyll  at 
present  not  understood. 

Action  of  Excessive  Heat. — Too  high  a  temperature 
also  arrests  or  perverts  all  the  functions  of  the  leaf. 
Where  transpiration  is  excessive,  and  the  absorption  of 
fresh  supplies  not  in  proportion,  the  leaves  speedily 
wither,  as  maybe  seen  in  a  field  of  mangels  on  a  hot  day, 
when  the  evaporation  of  watery  vapor  from  the  surface 
is  greater  than  the  absorption  of  moisture  by  the  root. 
On  the  other  hand,  during  the  night,  while  the  roots  are 
still  at  work,  the  transpiring  power  of  the  leaf  is  lessened, 
and  drops  of  water  exude  from  the  leaves.  Where  the 
temperature  is  so  high  as  to  kill  the  plant  or  leaf  out- 
right, it  is  the  protoplasm  which  dies  ;  its  constitution 
and  molecular  construction  become  changed,  its  power 
of  absorbing  water  destroyed,  and  thus  the  turgid  condi- 
tion of  the  cells  is  lost. 

Defensive  Arrangements. — Prejudicial  effects,  either 
of  a  too  low  or  a  too  high  temperature,  are  moderated 
by  the  conformation  of  the  leaf,  the  thickness  of  its  skin, 
the  arrangement  of  its  tissues,  the  presence  of  hairs,  and 
other  structural  endowments.  These  circumstances  ren- 
der the  selection  of  the  particular  variety  most  suitable 
for  any  special  locality  a  matter  of  the  greatest  moment. 
In  the  case  of  wheat,  for  instance,  some  varieties  are 
much  more  tender  than  others.  Bearded  wheats  are  as 
a  rule  hardier  than  the  beardless  ones.  A  variety  known 


66  PLANT  LIFE   OX   THE  FARM. 

as  the  Blood  Bed  is  very  hardy,  owing  its  immunity  possi- 
bly to  it's  habit  of  keeping  its  leaves  close  to  the  ground 
during  the  winter  and  spring,  and,  therefore,  less  exposed 
to  sudden  changes  of  temperature.  In  any  case,  its 
leaves  are  more  likely  to  be  protected  by  a  coating  of 
snow.  The  selection,  therefore,  of  the  kind  of  wheat 
best  adapted  for  Scotland,  for  the  eastern  or  for  the 
western  counties  of  England  respectively,  is  a  matter  of 
great  consequence.  A  variety  which  succeeds  in  a  warm 
moist  climate  would  be  quite  unsuitable  for  a  drier  one, 
even  if  the  temperature  sometimes  rose  higher. 

In  moist  air  it  has  lately  been  shown  by  M.  Vesque 
that  the  leaves  are  both  thinner  and  longer  than  when 
grown  in  dry  air,  that  the  vascular  bundles  of  the  stem 
are  also  thinner,  and  less  perfectly  developed  than  in 
dry  air.  Thus,  the  effects  of  a  saturated  atmosphere  on 
the  growth  of  leaves  seem  to  be  very  similar  to  those 
mentioned  by  Rauwenhof  as  characteristic  of  plants 
grown  in  obscurity.  When  fully  exposed  to  the  light, 
in  a  dry,  hot,  stagnant  atmosphere,  where  transpiration 
from  the  surface  of  leaves  is  ample,  the  leaves  become 
thicker,  their  anatomical  structure  is  altered,  and  they 
show  a  tendency  to  become  more  hairy. 

It  would  not  be  worth  while  for  the  agriculturist  to 
try  and  make  his  plants  adapt  themselves  to  different 
conditions  as  the  experimentalists  and  physiologists  do, 
but  the  indications  and  facts  brought  forward  by  the  lat- 
ter may  very  profitably  influence  the  farmer's  selection 
of  the  particular  varieties  best  suited,  by  their  conforma- 
tion or  structure,  to  meet  the  vicissitudes  of  particular 
localities. 

The  Influence  of  Contact  on  Leaves.— This  may  be 

dismissed  with  a  few  words  only,  as  it  is  not,  so  far  as  at 
present  known,  of  much  practical  importance  to  agricul- 
turists. In  addition  to  the  movements  immediately  con- 


SENSITIVENESS.  6? 

nected  with  growth,  gravitation,  or  the  action  of  light, 
which  are  manifested  only  during  active  growth,  there 
are  others  which  occur  in  the  fully-developed  leaf,  as  the 
periodical  night  and  day  movements,  the  movements  af- 
fected by  light  and  temperature,  and  lastly,  those  which 
are  caused  by  mechanical  contact,  as  by  the  impact  of 
certain  nitrogenous  substances,  as  in  the  so-called  car- 
nivorous leaves  before  referred  to,  and  those  caused  by  a 
touch  or  other  mechanical  eifect,  as  in  the  leaves  of  the 
sensitive  plant.  Chloroform  and  ether  arrest  these  move- 
ments, while  they  have  no  effect  upon  the  movements 
that  are  due  to  light  and  heat.  The  cause  of  the  move- 
ments in  question  is  attributed  to  the  sudden  contraction 
of  the  protoplasm,  the  expulsion  of  the  watery  contents 
of  the  cells  forming  the  lower  portion  of  the  swelling 
which  leaves  endowed  with  this  property  possess  at  the 
base  of  their  stalks.  The  cells  so  emptied  become  flaccid, 
and  the  leaf  in  consequence  falls.  The  water  expelled 
from  the  interior  of  the  cells  passes  into  the  spaces 
between  them  and  into  the  stem,  as  in  the  case  of  frozen 
leaves  (p.  65),  and  is  re-absorbed  when  the  irritation 
ceases.  The  balance  being  restored,  the  leaf  resumes  its 
horizontal  position. 

The  Action  of  Gravity  on  Stems,— The  cause  of  the 
upward  growth  of  stems,  though  so  familiar,  is  not 
understood.  It  is  in  general  exerted  in  opposition  to  the 
direction  of  gravitation.  If  a  stem  be  bent  downwards, 
growth  takes  place  much  more  rapidly  on  the  lower  sur- 
face, tending  to  make  it  convex  on  the  lower  surface,  and 
consequently  to  raise  its  free  end  (see  p.  54).  It  is  this 
tendency,  which,  as  has  been  previously  stated,  permits 
the  stalks  of  the  wheat  when  laid  to  recover  their  erect 
position.  Some  stem  or  portions  of  stem  are,  however, 
directly  influenced  by  gravitation,  as  in  the  case  of  under- 
ground stems  and  branches,  which  burrow  in  the  ground 


68  PLANT  LIFE   02ST  THE   FAKM. 

to  produce  tubers  ;  and  it  is  clear,  from  the  position  and 
direction  of  the  branches  of  a  tree,  that  the  influence  of 
gravity,  direct  or  negative,  varies  greatly  in  different 
cases,  so  that  on  the  whole  it  is  probable  that  the  direc- 
tions in  question  are  more  especially  due  to  varying  de- 
grees of  intensity  of  growth  in  different  situations,  accord- 
ing to  local  necessities  and  the  action  of  light,  than  to 
gravitation  pure  and  simple. 

Influence  of  Light  on  Stems.  —  The  remarks  made 
under  the  corresponding  heading  in  regard  to  leaves, 
apply  with  the  necessary  modifications  to  stems.  The 
stems  have  often  a  marked  tendency  to  move  or  grow 
towards  the  light,  but  the  opposite  tendency  is  shown  in 
other  instances,  as  in  the  ivy,  the  runners  of  the  straw- 
berry, and  other  cases,  where  this  peculiarity  favors  the 
application  of  the  stem  to  the  surface  of  the  ground,  of 
a  wall,  or  of  any  means  of  support,  as  in  many  climbing 
plants. 

The  action  of  light  in  retarding  growth,  already  referred 
to,  seems  opposed  to  many  of  the  phenomena  just  recorded 
— such  as  the  bending  of  the  stems  towards  the  light, 
the  fact  that  stems  grow  by  day  as  well  as  by  night,  the 
circumstance  that  the  tissues  of  plants  grown  in  the  dark 
are  feeble  and  ill-developed.  These  apparent  contradic- 
tions may  be  explained  by  the  fact  that  the  retarding 
influence  of  growth,  which  is  so  manifest  when  the  plant 
is  grown  under  artificial  conditions,  when  the  influence 
of  other  agencies  is  prevented  or  excluded,  is  compensated 
for  or  overcome  by  other  agencies — temperature,  moisture, 
etc. — when  the  plant  is  grown  under  natural  conditions. 
Again,  what  is  called  the  "after  effect  "has  to  be  con- 
sidered— the  facilities  for  growth  afforded  by  the  absence 
of  light,  by  the  agency  of  heat,  or  other  forces,  may  con- 
tinue after  those  influences  have  ceased  to  act,  and  so  a 
plant  may  grow  for  a  time  under  adverse  influences  by 


SENSITIVENESS.  69 

reason  of  the  impetus  gained  when  circumstances  were 
more  favorable. 

Influence  of  Heat  and  Moisture  on  the  Stem,— The 
growth  of  the  stem  is  directly  influenced  by  heat,  there 
being  in  this  as  in  other  cases  a  minimum  below  which 
growth  cannot  take  place,  an  optimum  at  which  it  takes 
place  most  vigorously,  and  a  maximum  beyond  which 
heat  is  injurious.  The  favorable  influence  of  heat  it  is 
which  in  part  overcomes  the  influence  of  gravitation,  and 
enables  the  stem  to  ascend.  The  stem  will  grow  fastest 
and  strongest  on  the  side  most  exposed  to  the  heat,  if 
that  heat  be  not  excessive,  and  this  tendency  will  remove 
it  from  the  soil.  Similarly  a  moist  condition  of  the  at- 
mosphere favors  growth,  and  the  stem  will  grow  the  fas- 
ter on  the  side  most  exposed  to  the  moist  vapor,  and, 
owing  to  the  convexity  so  formed,  it  will  in  consequence 
bend  its  free  end  and  its  concavity  towards  the  drier  side. 

Influence  of  Contact  on  Stems— Climbing  Plants,— 

The  most  marked  instance  of  this  occurs  in  the  case  of 
climbing  plants.  We  have  already  seen  that  the  young 
growing  parts  of  plants  very  generally  exhibit  gyratory 
movements,  these  movements  being  produced  by  inequali- 
ties of  growth,  now  in  this  direction,  now  in  that,  the 
result  being  that  the  free  end  moves  round,  and  that 
these  movements  are  only  indirectly  aifected  by  tempera- 
ture or  light.  In  the  case  of  climbing  plants,  such  as 
the  hop,  the  dodder,  the  tendrils  of  the  pea  or  of  the 
vine,  which,  are  peculiarly  sensitive  to  contact,  these 
movements  are  much  more  marked,  the  object  being  to 
secure  a  suitable  means  of  attachment,  and  so  to  expose 
the  leaves  when  present  to  the  influence  of  light  and  air 
with  the  least  expenditure  of  force  and  tissue.  Such, 
plants,  in  fact,  depend  upon  others  for  their  mechanical 
support.  When  the  free  end  of  such  a  plant  or  a  tendril 


70  PLAHT  LIFE  OK  THE  FARM. 

comes  -  into  contact  with  the  straw  of  a  wheat  plant, 
growth  is  checked  on  the  surface  by  which  contact  is 
made,  while  it  is  increased  on  the  opposite  side.  As  a 
consequence,  one  side  of  the  climber  is  flattened  against 
the  supporting  plant,  while  the  other  side,  growing  more 
rapidly,  becomes  convex,  and  its  tip  is  forced  in  process 
of  growth  round  the  supporting  stem.  The  increased 
growth  on  the  convex  side  of  the  coil  is  thus  the  direct 
outcome  of  the  impression  produced  by  contact. 

Combined  Effect   of  the   Preceding  Causes.  —  The 

effects  of  light,  heat,  gravitation,  etc.,  on  growing  plants 
are  thus  seen  to  be  manifold,  and  when  considered  sepa- 
rately seem  often  conflicting  and  contrary  to  common 
experience.  The  reason  is  that  under  natural  conditions 
the  one  influence  counteracts  the  other,  the  growth  of 
the  plant  being  the  outcome  of  the  combined  effect  of  all 
the  causes  alluded  to,  and  of  the  operation  at  one  time, 
and  under  one  set  of  circumstances,  of  the  influence  of 
one  agency  (controlled  or  not  by  others),  at  another  time 
of  a  different  agency.  This  affords  an  explanation  of 
the  fact  that  the  seasons  marked  by  extraordinary  pro- 
ductiveness are  not  those  wherein  some  one  or  more  of 
the  conditions  have  been  specially  favorable  at  a  particu- 
lar time,  even  though  that  time  be  the  growing  period, 
but  those  in  which  the  conditions  have  been  generally  pro- 
pitious throughout.  The  physiologist  endeavors  to  isolate 
the  agencies  which  influence  growth  in  order  to  ascertain 
precisely  what  each  does  independently  of  the  others  ; 
the  practical  man  has  to  deal  with  the  combined  effect  of 
all,  but  it  is  clear  that  the  combination  cannot  be 
properly  understood  unless  the  separate  effect  of  each 
component  be  first  clearly  comprehended. 


CHAPTER   V. 
DEVELOPMENT. 

Progressive  changes  during  growth. —Morphological,  physical,  and  phy- 
siological.—  Influence  of  inheritance. — Variation. —  Selection. — Re- 
serve-materials :  their  formation  and  transport.  —  Germination.  — 
Maturation. — Ripening  of  fruits  and  seeds. 

Development  as  here  understood  includes  those  pro- 
gressive changes  of  form  and  appearance  which  accom- 
pany the  growth  of  a  plant  from  an  infantile  to  an  adult 
state.  It  forms  no  part  of  our  present  plan  to  pursue 
this  part  of  the  subject  here,  as  any  elementary  text-book 
contains  sufficient  details  as  to  the  progressive  organiza- 
tion of  flowering  plants.  Growth  considered  separately 
results  in  increase  of  bulk  only,  but  development  includes 
the  whole  cycle  of  changes  which  convert  an  atom  of 
homogeneous  protoplasm  into  a  tree  laden  with  fruit  or 
into  a  wheat  plant  heavy  with  golden  ears.  A  mangel  or 
a  turnip  which,  under  favorable  circumstances,  gets  big- 
ger and  bigger,  may  be  said  to  grow.  It  increases  in  size 
and  weight,  but  neither  its  outward  appearance  nor  its 
internal  construction  is  otherwise  much  affected.  The 
giant  mangels  exhibited  at  root  shows  illustrate  growth 
rather  than  development.  They  are  very  big,  but  their 
nutritive  power  is  by  no  means  in  proportion  to  their 
size,  as  the  quantity  of  nutritive  matter  developed  is 
small  indeed  as  compared  with  the  great  quantity  of 
water  they  contain.  Growth,  in  fact,  is  but  the  prepara- 
tory stage,  during  which  material  and  machinery  are 
acquired,  to  be  turned  to  subsequent  use  in  the  consoli- 
dation of  the  stem,  the  construction  of  flower  and  seed, 
the  formation  and  storage  of  reserve  food-materials,  of 
starch,  of  oil,  of  the  various  secretions,  such  as  the 
caoutchouc,  the  alkaloids,  as  quinine,  morphia,  and  many 
others. 

(71) 


72  PLANT  LIFE  ON  THE  FARM. 

Growjth  and  development  may  go  on  together  at  the 
same  time,  as  we  see  in  an  oak  tree,  which  puts  forth  its 
midsummer  shoots  at  the  same  time  that  it  is  ripening 
its  acorns  and  consolidating  the  new  wood ;  but  in  an 
herbaceous  plant,  like  the  wheat,  as  development  pro- 
ceeds growth  ceases— at  least,  to  a  great  extent.  So  in 
the  case  of  such  plants  as  the  turnip,  the  mangel,  and 
the  hop,  when  the  plant  commences  to  enter  upon  the 
flowering  stage,  then  changes — not  merely  of  bnlk,  but 
of  outward  form,  and  to  some  extent  of  inward  construc- 
tion and  chemical  composition — occur.  So,  as  the  soft 
tissues  harden  into  solid  wood  by  deposit  of  woody  mat- 
ter in  their  wood  cells,  development  takes  place  ;  and,  as 
the  water  and  the  salts  taken  up  by  the  roots  and  the 
gases  inspired  by  the  leaves  act  and  re-act  upon  one 
another — aided  or  not,  as  the  case  may  be,  by  the  agency 
of  light — various  changes  occur  which  may  be  included 
under  the  head  of  development.  Development,  then,  is 
morphological  in  so  far  as  it  relates  to  the  conformation 
of  the  plant,  chemical  or  physical — in  so  far  as  it  includes 
the  chemical  and  physical  changes  which  accompany  the 
passage  from  the  young  to  the  old,  from  the  crude  and 
imperfect  to  the  complete  and  mature.  The  conditions 
which  favor  development  in  the  sense  here  understood 
are  thus  more  or  less  opposite  to  those  which  foster 
growth.  Gardeners  recognize  this  by  affording  plenty  of 
water  and  sufficient  heat  to  their  plants  when  growing, 
and  by  reducing  the  amount  of  water  as  the  plant  is  about 
to  produce  flower,  fruit,  and  seed.  They  apply  liquid 
manure  in  the  growing  stage,  but  withhold  it  in  the 
ripening  period.  They  root-prune  their  fruit  trees  when 
growth  is  too  vigorous  and  fruit  production  too  scanty. 
They  check  rampant  growth  by  keeping  the  roots  in 
small-sized  pots.  The  farmer  unfortunately  has  not  the 
same  control  over  his  plants  that  the  gardener  has,  but 
he  is  careful  as  to  the  time  when  he  applies  manure.  He 


DEVELOPMENT.  73 

is  not  particularly  distressed  at  a  wet  growing  season,  but 
he  looks  forward  with  hope  to  a  relatively  dry,  hot  period 
for  the  corn  to  ripen.  Of  great  practical  importance  also 
is  it  to  note  the  different  effects  of  manures  as  particularly 
observed  at  Kothamsted  ;  some,  such  as  nitrogenous  ma- 
nures, stimulating  growth  more  especially  ;  others,  such 
as  the  alkalis  and  superphosphates,  being  more  particu- 
larly favorable  to  the  ripening  of  the  seed  or  the  consoli- 
dation of  the  straw  by  the  formation  of  woody  fibre. 

Growth  is  the  same  throughout  all  plants,  but  the 
mode  of  development  is  much  more  specialized.  In  its 
initial  stages,  the  atom  of  protoplasm  that  is  to  be  the 
future  potato  plant,  is  not  appreciably  different  from 
that  which  is  destined  to  grow  into  a  wheat  plant  or  into 
a  fruit  tree.  While  growth  is  common  to  all  plants  and 
uniform  in  character,  development  is  special  and  different, 
less  or  more,  in  the  case  of  each  particular  species  or  kind 
of  plant.  Outward  conditions  greatly  influence  the 
amount  of  growth,  while  they  have  relatively  less  influ- 
ence on  the  extent,  still  less  on  the  direction  of  develop- 
ment in  the  individual  plant. 

Inheritance. — A  particular  kind  of  plant,  therefore, 
may  retain  its  characteristics  year  after  year,  century 
after  century,  age  after  age,  if  the  conditions  are  not 
greatly  altered,  because  the  successor  follows,  in  the 
course  of  its  development,  the  same  lines  as  its  predeces- 
sor did.  It  is  thus  by  hereditary  transmission  that  the 
characters  of  plants  are  perpetuated. 

Variation— Selection, — But  the  course  of  development 
in  the  offspring  is  not  always  and  in  all  cases  the  same  as 
in  the  parents.  On  the  contrary,  there  is  a  certain  range 
of  variation,  by  virtue  of  which  a  seedling  plant  does  not 
exactly  reproduce  either  of  the  parental  forms  ;  indeed, 
as  it  is  of  mixed  origin,  it  could  not  be  expected  to  do  so. 
4 


74  PLANT  LIFE  OK  THE  FARM. 

The  limits  of  variation  no  one  can  tell ;  sometimes  they 
seem  very  narrow  ;  at  other  times  we  know  them  to  be 
very  wide.  Within  short  periods  of  time  the  amount  of 
variations  may  be  inappreciable.  Within  geological 
periods  the  variation  in  the  course  of  development  is 
sometimes  so  enormous  that,  were  there  not  evidence  of 
the  fact,  it  would  be  difficult  to  connect  the  plants  and 
animals  that  have  gone  before  with  those  which  now 
exist.  Living  plants,  then,  are  influenced  in  the  course 
of  their  development  by  two  somewhat  antagonistic  prin- 
ciples— the  hereditary  principle  which,  on  the  whole, 
tends  to  keep  plants  as  they  are,  and  the  tendency  to 
vary,  which  is  the  source  of  that  variation  in  character 
which  enables  plants  and  animals  gradually  to  become 
adapted  to  altered  circumstances.  This  is  beneficial  to 
the  cultivator,  by  affording  him  an  opportunity  of  select- 
ing the  varieties  best  suited  for  his  purpose.  It  is  by 
exercising  selection  of  this  kind  that  Mr.  Hallett  suc- 
ceeded in  raising  his  "Pedigree  Wheat."  He  simply 
selected  for  sowing  the  best  grains  from  the  largest  and 
best  ears,  and  repeated  the  process  year  after  year,  just 
as  the  gardener  has  done  for  countless  generations  in  the 
case  of  fruits  and  .seeds,  as  the  cattle-breeder  does  with 
Shorthorns  or  other  pedigree  animals.  These  processes 
the  farmer  might  with  great  advantage  practice  to  a 
much  greater  extent  than  he  usually  does,  and  thus  se- 
cure hardy  productive  varieties  best  suited  to  his  particu- 
lar conditions  and  best  likely  to  fulfil  his  requirements. 

Formation  of  the  Embryo,— The  two  processes  of 
growth  and  development  may  also  be  illustrated  by  recall- 
ing what  takes  place  in  the  germination  of  a  seed.  A 
ripe  seed  contains  within  its  coat  or  husk  an  embryo 
plant.  Very  often  that  embryo  plant  is  invested,  as  in 
the  case  of  the  grain  of  wheat,  with  a  whitish,  floury 
substance,  known  as  the  "perisperm."  All  grass  seeds 


DEVELOPMENT.  75 

have  this  perisperm  surrounding  their  embryo.  A  simi- 
lar substance  is  found  in  the  seeds  of  mangel  ;  the  seeds 
of  turnips,  peas,  beans,  and  clover,  on  the  other  hand, 
are  destitute  of  it.  An  embryo  plant  consists  of  a  radi- 
cle, or  rudimentary  root,  surmounted  by  a  caulicle, 
which  is  often  so  short  as  to  be  imperceptible  to  the 
naked  eye,  but  from  which  spring  the  seed-leaves,  or 
cotyledons — one  only  in  the  case  of  all  the  cereals  and 
grasses,  two  in  the  case  of  the  other  crops  of  the  farm. 
In  the  case  of  the  wheat  grain,  where  the  perisperm  is 
abundant,  the  cotyledon  is  small  and  thin ;  but  in  the 
pea  or  bean,  where  the  perisperm  is  absent,  the  cotyle- 
dons are  very  thick  and  fleshy.  The  difference  depends 
upon  the  presence,  in  the  one  case,  of  large  quantities  of 
reserve-materials  in  the  embryo  itself,  while  in  the  case 
of  the  wheat  the  reserve-materials  are  stored  up  in  the 
perisperm. 

The  seed,  then,  in  addition  to  the  young  plant,  con- 
tains in  the  tissues  of  the  embryo  plant  itself,  or  in  the 
perisperm  surrounding  it,  reserve -materials  destined  to 
supply  the  young  plant  with  food  during  its  growth  and 
development. 

Reserve-materials:  their  Transport.  — Under   the 

head  of  nutrition,  mention  has  been  made  of  the  sub- 
stances formed  in  plants  through  various  agencies.  Some 
of  these  are  used  up  at  once  during  growth,  while  others 
are  reserved  for  future  use,  having  usually  undergone 
some  change  in  constitution  to  fit  them  for  their  purpose. 
Speaking  broadly,  these  reserves  are  either  starchy,  oily, 
or  albuminoid  (nitrogenous)  in  their  character.  The 
starchy  or  oily  ingredients  are  the  direct  products  of  the 
action  carried  on  under  the  influence  of  sun  light  in  the 
cells  containing  chlorophyll.  Starch  cannot  be  formed 
in  cells  containing  no  chlorophyll,  nor,  for  a  continuance, 
in  chlorophyll-containing  cells,  unless  they  are  exposed 


76  fLAKT  LIFE  OK  THE  FARM. 

to  the  light.  The  starch  in  a  wheat  grain,  for  instance, 
is  not  actually  formed  within  the  seed — it  is  formed  in 
the  leaves  and  conveyed  from  them  to  the  seed.  But 
starch  is  insoluble  ;  therefore,  before  it  can  be  conveyed 
from  the  place  where  it  is  formed  to  the  place  where  it  is 
to  be  stored,  it  must  be  rendered  soluble,  and  this  change 
is  effected  by  a  process  of  fermentation  resulting  in  its 
conversion  into  soluble  "  glucose."  Arrived  at  the  seed, 
the  glucose  is  turned  back  into  insoluble  starch  to  be 
reserved  for  use  when  required.  The  process  is  essentially 
the  same  in  the  case  of  the  tuber  of  the  potato,  the 
"bulb"  of  the  turnip,  or  the  root  of  the  mangel.  All 
these  organs  are  severally  storehouses  wherein  food  is  ac- 
cumulated for  future  use.  The  food  is  neither  made  nor 
elaborated  in  them,  but  simply  stored,  having  been 
formed  in  the  leaves  and  conveyed  to  the  storehouse. 
At  one  time,  therefore,  the  leaves  and  stem  may  be  full 
of  starch,  at  another,  they  may  be  destitute  of  it,  owing 
to  its  having  been  transferred  to  the  seed  or  the  bulb. 

While  the  origin  of  the  starch  is  now  well  known  and 
the  processes  connected  with  its  formation  and  transport 
fairly  understood,  it  is  not  so  with  the  nitrogenous  mat- 
ters. The  nitrogen,  as  we  have  seen,  enters  the  plant  by 
the  root,  and  is,  therefore,  not  directly  dependent  on 
light  or  chlorophyll  action.  Nitrogenous  compounds  are 
not  formed  in  the  seed,  but  conveyed  to  them  just  as  the 
starch  is. 

The  carbonaceous  reserve-materials — that  is,  the  starch, 
the  sugar,  the  oil,  the  coloring  matters — are  all  the  direct 
result  of  the  action  of  the  green  matter  acted  on  by  light; 
the  starch  and  the  sugar  are  essential  requisites  for  the 
building  up  of  the  cell-membrane,  the  albuminoid  or 
nitrogen-containing  substances  being,  in  their  turn,  es- 
sential to  the  formation  of  the  protoplasm,  and  of  the 
chlorophyll. 


DEVELOPMENT.  77 

Germination* — The  conditions  under  which  germina- 
tion takes  place  need  not  be  alluded  to  at  any  length,  as 
they  are  the  same  as  those  requisite  for  growth,  and 
practically  every  cultivator  knows  that  air  (oxygen), 
moisture,  and  heat,  varying  in  amount  according  to  the 
plant  and  according  to  circumstances,  are  required,  and 
that  his  success  depends  in  great  measure  upon  the 
proper  tillage  of  the  soil  which  secures  these  requisites. 
When  the  seed,  or  rather  the  embryo  plant  within  it, 
begins  to  grow,  water  is  absorbed,  the  seed  swells,  the 
insoluble  starch  stored  up  becomes  converted  into  glu- 
cose, or  a  form  of  sugar,  by  the  agency  of  a  nitrogenous 
substance  which  acts  as  a  ferment.  These  chemical  pro- 
cesses are  accompanied  by  an  evolution  of  heat  and  an 
outpouring  of  carbonic  acid  gas.  Thus  is  it  that  in  malt- 
ing barley  the  grain  swells,  gets  hot,  and  its  starch  is 
converted  into  sugar.  As  the  seedling  grows,  both  starch 
and  sugar  gradually  disappear,  although  the  stock  of 
starch  is  continually  replenished  so  long  as  the  leaves 
continue  to  act.  The  nitrogenous  constituents  of  the 
seed  undergo  similar  changes  from  the  insoluble  to  the 
soluble  condition,  the  latter  being  capable  of  transport 
from  place  to  place  as  may  be  required. 

The  accumulation  of  insoluble  matter  in  the  seeds  is 
accounted  for  by  M.  Deherain  in  this  wise.  At  the  period 
of  maturation  the  juices  of  the  plant  contain  the  various 
substances  held  in  solution.  These  juices  are  directed 
towards  the  seed  or  towards  the  store  organs,  wherein,  by 
virtue  of  some  changes  not  fully  understood,  the  matters 
previously  held  in  solution  become  as  it  were  precipitated 
and  rendered  for  the  time  insoluble.  As  a  consequence, 
the  water  is  deprived  of  these  materials,  and  to  restore 
the  balance  fresh  supplies  are  drafted  from  the  leaves 
towards  the  store-organs,  there  in  like  manner  to  deposit 
their  starch,  their  inulin,  or  albuminoid  matter.  In  the 
case  of  biennials  like  turnips,  or  mangels,  during  the 


78  PLANT  LIFE   ON  THE   EABM. 

first  season  of  growth,  the  leaves  collect  and  form  the 
nutritive  matters  which  are  subsequently  transferred  to 
the  "  root,"  and  the  store  so  accumulated  is  utilized  the 
following  season  in  the  formation  of  flowers  and  seeds,  as 
before  explained. 

Growth,  then,  in  a  chemical  sense,  may  be  said  to  con- 
sist in  the  absorption  of  the  raw  materials  for  the  food  of 
plants — development,  in  a  chemical  sense,  may  be  taken 
as  including  the  various  transformations  which  those 
raw  materials  undergo  to  fit  them  for  the  nutrition  of 
the  plant,  or  the  formation  of  reserve-materials  to  be 
stored  up  for  future  use.  The  history  of  these  develop- 
mental changes  is  a  matter  for  the  chemist  to  clear  up 
with  the  aid  of  chemical  re-agents,  used  both  with  and 
without  the  help  of  the  microscope.  It  is  in  this  de- 
partment of  physiology  that  our  knowledge  is  at  present 
most  imperfect. 

Maturation. — The  foregoing  facts  and  phenomena  have 
been  brought  to  light  principally  by  chemical  analysis  of 
the  same  kind  of  plant  at  different  times  and  in  different 
stages  of  its  growth,  and  particularly  by  the  analysis  of 
different  parts  of  the  same  plant,  some  young,  some  old. 
In  the  case  of  wheat,  it  was  ascertained  by  Messrs.  Lawes 
and  Gilbert  that  during  the  five  weeks  beginning  with 
June  21,  there  was  but  little  accumulation  of  nitrogen  in 
the  plant,  while  during  the  same  period  more  than  half 
the  total  carbon  was  accumulated.  The  building-up 
process  was  thus  going  on  more  quickly  than  that  of 
maturation.  In  this  manner  it  has  also  been  found,  not 
only  that  the  starchy  and  the  albuminous  matters  under- 
go changes  and  disappear  from  the  leaves,  but  that 
mineral  matters  and  salts,  such  as  phosphates  and  salts 
of  potash,  which  at  one  stage  of  growth  abound  in  the 
leaves,  at  another  time  are  almost  entirely  absent  from 
them,  but  are  found  in  abundance  elsewhere.  The  mi- 


DEVELOPMENT.  79 

gration  of  these  elements  has  been  well  studied  in  the 
case  of  the  wheat  by  M.  Isidore  Pierre,  who  has  conclu- 
sively shown  that  what  the  leaves  lose  in  these  respects 
is  gained  by  the  ear.  One  important  feature  of  matura- 
tion then  consists  in  the  gradual  cessation  of  the  work 
done  in  the  leaf,  the  exhaustion  of  its  supplies — carbo- 
naceous, nitrogenous,  and  mineral — and  the  transport  of 
these  materials  to  the  organs  of  reserve,  to  the  bark  and 
young  wood  of  the  tree,  to  the  seed  in  the  case  of  wheat 
and  other  annuals,  to  the  roots,  bulbs,  and  tubers  in 
other  cases.  In  the  case  of  an  annual  herbaceous  plant 
like  the  wheat  it  appears  that  both  root-action  and  leaf- 
action  become  reduced  to  a  minimum,  or  are  even 
altogether  stopped  some  two  or  three  weeks  before  the 
wheat  is  ready  to  cut,  so  that  during  that  period  no  in- 
crease of  weight  of  the  plant  as  a  whole  takes  place  ;  and 
if  the  ears  themselves  increase  in  weight,  it  is  because 
they  derive  matter  from  other  parts  of  the  plant,  which 
diminish  in  weight  in  proportion.  A  few  figures  cited 
by  M.  Deherain  Avill  illustrate  the  truth  of  these  remarks 
— thus  in  the  case  of  colza,  out  of  a  total  of  one  thousand 
parts  (grammes)  of  phosphoric  acid  in  the  entire  plant, 
four  hundred  and  fifty-six  were  found  in  the  leaves  in 
March,  and  only  twenty-five  in  the  leaves  in  June,  while 
the  flowering  stems  at  the  latter  period  contained  eight 
hundred  and  sixty.  Results  of  a  similar  character  might 
be  quoted  in  the  case  of  potash  and  albuminoid  matters. 
In  all  cases  while  the  relative  proportions  gradually  de- 
cline in  the  leaves  they  become  correspondingly  augment- 
ed in  the  flowering  part  of  the  stem  and  in  the  seeds. 

These  results  are  attributed  by  M.  Deherain  in  great 
degree  to  varying  degrees  of  evaporating  power  possessed 
by  the  leaves.  According  to  him,  the  older  leaves  at  the 
base  of  the  stem  evaporate  but  little  as  compared  to  the 
younger  leaves  near  the  top.  These,  by  their  superior 
evaporating  power,  cause  the  lower  parts  to  be  emptied 


80  PLANT  LIFE   ON  THE   FARM. 

of  their  contents,  which  are  thus  forced  upwards  towards 
the  upper  part  of  the  stem.  In  a  yery  dry,  hot  season, 
when  the  light  is  intense,  evaporation  and  life-action 
generally  go  on  too  rapidly,  and  the  harvest  is  deficient ; 
on  the  other  hand,  if  the  summer  is  wet  and  the  light 
deficient,  maturation  is  imperfect,  the  transport  of  nu- 
tritive matters  from  leaves  upwards  to  the  fruit  and 
seeds  is  checked,  the  younger  leaves  do  not  draw  upon 
the  lower  ones,  and  the  season,  though  favorable  to  for- 
age crops,  is  not  so  propitious  to  grain  crops,  to  fruit 
ripening,  or  to  timber  in  which  a  deposit  of  woody 
material  in  the  cells  is  essential. 

Ripening  of  Fruits. — The  ripening  of  fruits,  such  as 
those  of  the  apple  and  pear  is  attended  with  a  series  of 
chemical  changes  which  can  here  only  be  cursorily  allud- 
ed to.  While  the  fruit  remains  green,  it  acts  precisely 
as  a  leaf  does.  As  it  ripens  its  color  changes  ;  it  no  lon- 
ger decomposes  carbonic  acid  and  gives  off  oxygen  in  the 
daylight,  but  it  utilizes  the  oxygen  of  the  carbonic  acid 
to  oxidize  and  burn  up  the  vegetable  acid  and  the  sugar 
which  the  fruit  contains.  Subsequently  the  sugar  under- 
goes a  species  of  alcoholic  fermentation,  characterized  by 
the  emission  of  carbonic  acid  gas  and  by  the  formation 
of  alcohol,  which  latter,  uniting  with  the  acid  of  the 
fruit,  produces  ethers  of  various  kinds,  to  which  the 
peculiar  odor  and  flavor  of  the  fruit  are  due. 

The  processes  of  maturation  and  fruiting  therefore  are 
not  dependent  upon  the  mere  accumulation  of  food  ; 
otherwise  by  increasing  the  quantity  of  manure  and  ap- 
plying it  continuously  we  should  increase  the  crop.  As 
a  matter  of  fact  we  know  we  should  not  do  so,  and  that 
the  effect  of  over-feeding  under  such  circumstances  would 
be  to  render  the  plant  unhealthy  by  preventing  it  from 
assimilating  and  maturing.  Similarly  we  know  from  ex- 
perience that  heat  alone  is  not  sufficient  to  induce 


MULTIPLICATION.  81 

thorough  ripening,  but  that  exposure  to  light  is  also 
requisite,  a  dull,  cloudy  summer,  even  if  warm,  being 
unpropitious  to  ripening,  whether  of  fruit  or  grain. 


CHAPTER  VI. 
MULTIPLICATION. 

Sub-division. —  Intermarriage. —  Buds,  Branches,  Tillering,  Tubers. — 
Fertilization,  Stamens,  Anthers,  Pollen,  Pistil. — Mechanism  of  Fer- 
tilization. —  Cross-Fertilization.  —  Transport  of  Pollen.  —  Insect 
agency.— Self-Fertilization.— Fertilization  of  cereals.— Hybridiza- 
tion.— Germination. 

Multiplication. — There  are  two  special  ways  in  which 
plants  multiply.  One  is  a  mere  process  of  extension  or 
subdivision — a  modified  form  of  growth,  in  fact.  The 
other  is  the  result  of  the  union  or  commingling  of  a  por- 
tion of  the  protoplasm  of  one  plant  with  a  corresponding 
particle  of  another  plant.  In  the  lower  plants,  as  they 
are  designated,  it  is  not  even  necessary  that  union  of 
particles  of  protoplasm  from  different  plants  should  be 
effected.  The  contents  of  one  cell  blend  with  the  con- 
tents of  another  cell  on  the  same  plant,  and  the  result  is 
the  formation  of  a  seed  or  spore,  by  means  of  which  the 
plant  is  reproduced.  The  first  process  of  multiplication, 
by  division,  is  called  asexual,  the  second  sexual,  because 
it  is  a  process  of  intermarriage  requiring  the  co-operation 
of  two  distinct  particles  of  protoplasm.  In  the  very 
lowest  plants  these  two  particles  present  no  appreciable 
differences,  but  in  the  higher  plants  and  animals  they 
present  such  differences  as  to  enable  us  to  distinguish 
one  as  male,  the  other  as  female.  In  the  lowest  plant 
the  two  particles  are  split  off  from  the  same  mass  of  pro- 
toplasm, while  in  the  higher  plants  the  male  element  is 
formed  from  a  different  source  from  the  female. 


82  PLANT   LIFE   ON   THE   FAKM. 

Bud  Formation* — In  the  higher  perennial  plants, 
among  which  are  included  many  which  come  under  the 
notice  of  the  farmer,  asexual  multiplication  is  effected  by 
means  of  buds.  When  a  bud  is  to  be  formed,  growth  in 
length  is  checked,  the  stem  or  the  branch  ceases  length- 
ening, the  outer  leaves  often  become  reduced  to  a  scale- 
like  condition,  while  the  inner,  central,  and  younger 
ones  remain  in  an  undeveloped  state  until  the  warmth  of 
spring  calls  them  into  growth,  when  they  gradually 
lengthen  into  shoots,  as  in  fruit  and  timber  trees.  While 
the  buds  remain  fixed  to  the  trees  which  gave  them 
origin,  their  growth  and  development  is  a  process  of  ex- 
tention  or  branching  merely.  Similarly  the  process  of 
"  tillering  "  is  simply  due  to  the  formation  and  develop- 
ment of  buds  and  shoots  from  the  nodes  or  knots  at  the 
base  of  the  stem  of  the  wheat,  and  is  to  be  regarded  as  a 
process  of  branching  rather  than  of  actual  multiplication. 
Such  branches  are  formed  more  readily  in  proportion  as 
the  seed  is  not  buried  deeply.  The  same  process  of 
growth  which  is  desirable  in  a  cereal  or  in  clover  is 
highly  objectionable  in  the  case  of  "  weeds,"  such  as 
docks,  thistles,  and  plantains.  The  imperfect  measures 
often  taken  to  exterminate  these  often  tend  to  increase 
the  mischief  by  bringing  about  the  formation  of  many 
new  buds.  When  buds  become  detached  naturally,  or 
are  severed  from  the  parent  artificially  and  made  to  grow 
— as  when  a  gardener  takes  a  "  slip,"  "  buds"  a  rose,  or 
"grafts"  a  fruit  tree — the  process  is  really  one  of  multi- 
plication. So,  when  a  farmer  plants  a  "  seed  potato," 
which  yields  him,  it  may  be,  forty-fold,  he  really  plants, 
not  a  "  seed,"  nor  a  root,  but  a  peculiar  form  of  bud 
called  a  tuber. 

Tubers. — A  potato,  in  fact,  is  an  underground  branch, 
or  connected  series  of  buds,  forming  a  swollen  subter- 
ranean shoot,  In  this  are  stored  up  the  starch  and  other 


MULTIPLICATION.  83 

ingredients  necessary  for  the  nutrition  of  the  young 
potato  plants.  The  "  eyes "  of  the  potato  are  really 
buds,  as  any  one  may  see  for  himself  who  will  examine 
the  "chits"  of  a  sprouting  potato.  These  latter  bear 
the  same  relation  to  the  parent  tuber  that  the  shoots 
which  spring  from  the  old  "stools  "  in  a  coppice  or  from 
a  pollard  willow  do  to  the  trunk.  The  presence  of  these 
tubers  indicates  that,  under  natural  circumstances,  the 
plant  requires  a  long  period  of  rest.  To  this  end  food  is 
stored  in  the  tuber,  and  active  growth  ceases  for  a  time, 
until  again  excited  by  heat  and  moisture.  It  may  be 
inferred  from  this  that  continuous  growth,  were  it  possi- 
ble, would  be  injurious  because  the  climatal  conditions 
are  unsuited  for  it,  as,  indeed,  may  be  witnessed  in  the 
way  in  which  the  haulms  of  the  early  potatoes  are  injured 
by  spring  frost. 

Fertilization* — In  the  case  of  plants  grown  for  their 
fruit  or  seed,  as  in  the  case  of  wheat  and  cereals  generally, 
much  attention  has  naturally  to  be  paid  to  the  conditions 
which  favor  sexual  multiplication. 

The  morphological  characters  of  the  plants  undergo  a 
change.  In  general  terms,  it  may  be  said  that  the  growth 
of  the  stem  is  arrested,  and  the  growth  and  mode  of  de- 
velopment of  the  leaves  not  only  arrested,  but  more  or 
less  profoundly  modified,  so  as  to  form  the  parts  of  the 
flower.  All  parts  of  the  flower  are  constructed  on  the 
same  original  plan  as  leaves,  but  they  gradually  assume  a 
very  different  appearance  in  the  course  of  their  develop- 
ment to  fit  them  for  their  work  of  aiding  fertilization. 
It  is  not  necessary  in  this  place  to  enter  into  details  as  to 
the  floral  construction,  which  varies  in  different  plants  ; 
the  important  points  in  relation  to  our  present  subject 
are  the  stamens  and  the  pistils  and  their  contents. 

Within  the  green  scales  which  constitute  the  flower  of 


84:  PLANT   LIFE   OK   THE   FARM. 

wheat,  .within  the  butterfly-shaped  and  brightly-colored 
petals  of  the  pea  or  the  clovers,  and  the  yellow  petals  of 
the  flowers  of  the  turnip  or  the  colza,  the  rape  or  the 
mustard,  are  a  series  of  fine  thread-like  bodies,  the 
"  stamens,"  varying  in  number,  size,  and  arrangement  in 
different  flowers,  but  each  consisting  of  a  fine  thread  or 
stalk,  called  the  "  filament."  Surmounting  this  is  a  sort 
of  pocket  or  case,  called  the  "anther,"  containing  a  yel- 
low or  greenish  dust,  which,  when  examined  with  a  lens, 
is  seen  to  be  made  up  of  separate  cells  or  grains,  called 
the  pollen  grains.  Some  idea  of  the  number  of  these 
pollen  grains  may  be  gained  from  the  calculations  of  Mr. 
A.  S.  Wilson,  who  estimates,  from  the  actual  counting 
of  a  portion,  that  each  anther  of  rye  contains  twenty 
thousand  pollen  cells,  five  hundred  thousand  of  which 
are  needed  to  make  up  one  grain  in  weight.  A  floret  of 
spring  wheat  in  like  manner  was  found  to  contain  six 
thousand  eight  hundred  and  sixty-four  grains,  but,  as 
the  pollen  grains  of  the  wheat  are  larger  than  those  of 
the  rye,  only  three  hundred  and  ninety  thousand  are 
required  to  make  up  a  grain  weight.  An  acre  of  wheat 
may,  it  is  further  calculated,  produce  fifty  pounds  of 
pollen,  and  an  acre  of  rye  two  hundred  and  twenty-four 
pounds. 

Within  the  stamens,  in  most  flowers  with  which  farm- 
ers have  to  do,  is  a  "  pistil,"  consisting  of  a  thick  portion 
below,  which  contains  the  young  "ovule"  destined  to 
become  the  seed,  and  which  is  usually  overtopped  by  a 
little  thread,  called  the  "style,"  whose  upper  end,  again, 
is  dilated  into  a  "  stigma."  In  the  case  of  the  wheat  and 
other  grasses  these  stigmas  are  covered  with  fine  white, 
silky  hairs.  The  essential  constituents  of  the  flower, 
without  which  reproduction  cannot  be  effected,  are  the 
pollen  grains  and  the  ovule.  All  other  parts  of  the 
flower  are  mere  accessories,  and  some  of  them  are  very 


MULTIPLICATION.  85 

frequently  absent  without  the  process  of  reproduction 
being  impaired  by  their  absence. 

The  process  of  fertilization  may  be  described  in  general 
terms  as  follows  : — The  ovule  contains,  in  a  cell  just  be- 
neath the  skin  at  its  summit,  one  special  piece  of  pro- 
toplasm, the  "  germ,"  which  is  destined  to  develop  into 
the  embryo  plant.  The  pollen-cell  consists  of  an  outer 
coat  and  an  inner  lining  ;  the  outer  coat  bursts,  and  the 
inner  protoplasmic  lining  is  protruded  in  the  form  of  a 
tube,  which  passes  down  between  the  cells  of  the  stigma 
and  style,  growing  in  length  and  feeding  as  it  goes,  like 
a  parasitic  fungus,  on  the  contents  of  the  cells  of  the 
style,  until  it  reaches  the  ovule  and  comes  into  close 
proximity  to,  if  not  actually  into  contact  with  the  germ. 
In  consequence  of  this  action  a  cell- wall  is  formed  around 
the  germ,  which  latter  divides  and  subdivides  in  various 
directions,  the  result  of  the  subdivision  being  the  forma- 
tion of  an  embryo  plant,  as  mentioned  at  p.  74,  while 
the  ovule  covering  the  embryo  ripens  into  the  seed.  The 
germ  is  thus  fertilized  by  the  pollen  or  sperm-cell,  and 
unless  the  two  come  in  contact,  the  formation  of  the 
embryo  plant  does  not  take  place. 

Cross  Fertilization.— It  has  teen  mentioned  that  the 
flowers  with  which  the  farmer  is  concerned  have  for  the 
most  part  their  stamens  and  pistils  in  the  same  flower 
(hops  are  an  exception*),  and  therefore  they  may  be  de- 
scribed as  structurally  hermaphrodite.  It  does  not,  how- 
ever, follow  that  they  are  functionally  hermaphrodite — 
that  is,  that  the  pollen-grain  of  any  particular  flower 
fertilizes  the  germ-cell  of  the  same  flower.  As  a  matter 
of  fact,  the  reverse  usually  happens,  and  the  pollen  of 


*In  the  hop,  the  stamens  and  pistils  are  in  separate  flowers  upon 
different  plants.  The  farmer  in  the  United  States  will  find  that  the 
stamens  and  pistils  are  in  different  flowers  upon  the  same  plant  in  In- 
dian corn,  pumpkin,  squash,  and  all  other  plants  of  that  family. 


86  PLANT  LIFE   ON  THE   FARM. 

one  flower  exerts  its  influence,  not  upon  the  germ  of  its 
own  flower,  but  upon  that  of  another,  perhaps  situated 
on  some  other  plant.  Cross-fertilization  is  often  neces- 
sitated by  the  circumstance  that  while  the  pollen  of  any 
particular  flower  may  be  ripe,  the  stigma  and  the  germ- 
cell  of  the  same  flower  may  not  be  ripe  at  the  same  time, 
or  vice  versa,  and  in  such  case  the  co-operation  of  some 
other  flower  is  needed. 

Transport  of  Pollen.— It  becomes,  therefore,  needful 
to  ascertain  in  what  manner  the  pollen  is  carried  from 
one  flower  to  another.  This  is  effected  in  various  ways 
— sometimes  the  mere  splitting  of  the  anther  with  some 
degree  of  force  suffices  to  scatter  the  pollen,  at  other 
times  the  currents  of  air  suffice  to  waft  it  from  one  flower 
to  another,  while  at  other  times  insects  of  various  kinds 
convey  the  pollen  from  one  flower  and  deposit  it  on  the 
stigma  of  another. 

The  adaptations  of  floral  structure  to  insect-agency  in 
fertilization,  as  also  the  contrivances  for  excluding  unde- 
sirable visitors,  are  most  varied  and  most  remarkable, 
but  they  can  only  be  mentioned  here.  As  a  rule,  it  may 
be  stated  that  flowers  endowed  with  bright  colors,  irregu- 
lar construction  (like  that  of  the  pea  or  bean),  or  rich 
perfume  are  fertilized  by  insect  agency.  The  insects  are 
attracted  by  the  bright  colors,  the  perfumes,  and  the 
sweet  secretions  of  the  flower.  On  alighting,  they  are 
often  compelled  by  the  peculiar  construction  and  mech- 
anism of  the  flower  to  enter  or  leave  it  in  such  a  way 
that  they  must  in  the  one  case  brush  out  the  pollen,  and 
in  the  other  deposit  it  on  the  stigma.  It  will  be  noted 
how  this  process  of  cross -fertilization  favors  that  process 
of  variation  to  which  allusion  has  previously  been  made. 

The  farmer  wishing  to  keep  his  stock  of  seed  turnips 
pure,  knows  how  difficult  it  is  to  do  this,  not  only  be- 
cause cross-fertilization  is  the  rule  in  the  particular 


MULTIPLICATION.  87 

variety  he  wishes  to  grow,  but  also  because,  if  any  other 
variety  is  grown  in  the  neighborhood,  its  pollen  is  sure 
to  impregnate  his  variety  and  produce  a  mongrel  off- 
spring. Cross-fertilization  then  acts  in  antagonism  to 
the  hereditary  tendency,  and  secures  variation — and  not 
only  variation,  but  more  vigorous  and  robust  constitu- 
tion, and  more  numerous  and  more  healthy  descendants. 
Self-fertilization,  or  "in  and  in  breeding,"  occurs,  no 
doubt,  in  some  instances,  especially  in  cereal  grasses  ; 
and  there  are  indeed  many  cases  where,  for  various  rea- 
sons which  need  not  be  cited  here,  no  other  mode  of  fer- 
tilization is  possible.  Relative  permanence  of  character 
is  secured  by  this  means,  and  if  constitutional  vigor  and 
the  health  of  the  offspring  be  impaired  by  the  long  con- 
tinuance of  the  process,  these  ill-effects  are  provided 
against  by  the  circumstance  that  a  comparatively  trifling 
change  in  the  flower,  or  in  the  circumstances  by  which 
it  is  surrounded,  will  suffice  to  prevent  self-fertilization 
and  secure  cross-fertilization. 

Fertilization  of  Cereals, — It  has  very  generally  been 
stated  that  the  wind  is  the  special  agency  by  means  of 
which  the  pollen  is  carried  from  flower  to  flower  of  these 
plants,  and  no  doubt  this  is  true  to  some  extent  and  under 
certain  circumstances.  From  the  careful  experiments  and 
observations  of  Mr.  A.  S.  Wilson,  recorded  in  a  paper  read 
before  the  Botanical  Society  of  Edinburgh,  Scotland, 
and  printed  in  the  "  Gardener's  Chronicle,"  March  14, 
1874,  it  appears  that  self-fertilization  is  the  rule  among 
cereals,  though  cross-fertilization  does  occasionally  take 
place  and  has  been  effected  artificially  by  various  experi- 
menters. The  flowers  of  wheat,  barley,  and  oats  open  to 
a  slight  degree  and  allow  the  anthers  to  protrude,  often 
quite  suddenly  ;  but  whether  the  flowers  fully  or  but 
partially  open,  says  Mr.  W. ,  they  are  fertilized  before  the 
anthers  are  visible  outside.  "  The  Belgian  farmers,"  he 


88  PLANT   LIFE   ON   THE   FARM. 

continues,  "  who  trailed  ropes  over  their  flowering  wheat 
to  insure  complete  fertilization,  were  doing  that  which 
the  very  appearance  of  the  anthers  told  them  in  whispers, 
not  yet  heard,  had  already  been  accomplished."  The 
pollen  of  these  plants  which  the  winds  disperse,  is  not 
that  which  fertilizes,  but  that  which  is  not  required  for 
fertilization.  The  success  of  the  process  depends,  as 
before  said,  upon  the  circumstance  whether  or  not  the 
pollen  and  the  feathery  stigma  are  respectively  ripe  at 
the  same  time.  If  so,  then  fertilization  results  ;  if  not, 
there  is  still  a  chance  of  cross-fertilization,  but  if  that 
fail,  the  flower  remains  barren. 

Hybridization  is  a  procedure  with  which  the  gardener 
is  much  more  familiar  than  the  farmer.  It  is  only  a 
further  development  of  cross-fertilization.  Cross-fertili- 
zation, as  has  been  said,  takes  place  between  flowers  of 
the  same  individual  plant,  or  between  flowers  of  two  dif- 
ferent individuals  of  the  same  species  ;  but  hybridization 
is  effected  by  crossing  the  flowers  of  two  separate  species, 
as  in  the  case  of  the  Alsike  clover,  which  is  said  to  be  a 
hybrid  between  the  white  or  Dutch  clover  and  the  red 
clover. 

Chemical  Changes. — The  chemical  changes  which  oc- 
cur during  the  formation  of  the  flower,  and  especially 
during  the  ripening  of  the  seed,  have  already  been  alluded 
to.  The  contrast  between  the  composition  of  the  leaves 
and  that  of  the  pollen  and  of  the  seeds  is  very  striking, 
and  analysis  brings  out  the  fact  of  the  accumulation  of 
nitrogenous  and  phosphatic  and  mineral  matters  in  the 
pollen  and  in  the  seed.  In  haymaking  it  is  better,  if 
possible,  to  mow  before  the  leaves  are  exhausted  of  their 
contents  by  the  seeds,  or  at  any  rate,  before  the  latter  are 
shed.  If  cutting  be  delayed,  a  great  part  of  the  nutritive 
matter  is  withdrawn  from  the  leaves  and  stem  to  be 


THE   BATTLE   OF   LIFE.  89 

* 

stored  up  in  the  seeds,  which  fall  readily  when  ripe,  and 
thus  occasion  a  loss  to  the  farmer.  Again,  as  it  has  been 
shown  that  the  seeds  of  cereals  contain  their  full  propor- 
tion of  nutritive  matter  some  little  time  before  they 
would  be  considered  thoroughly  ripe,  early  cutting, 
where  practicable,  is  to  be  recommended  to  secure  the 
crop  and  obviate  possible  loss  from  delay. 


CHAPTER  VII. 
THE  BATTLE  OF  LIFE. 

Plants  considered  in  their  relation  to  theif  ^struggle  for  existence. — 
Effect  of  adverse  external  conditions.— Hostility  of  rivals,  Weeds. — 
Competition  of  fellows. —  Gregarious  vegetation. — Associated  or 
mixed  vegetation. — Alternate  vegetation,  rotation. — Objects  of  the 
cultivator  not  the  same  as  those  of  the  plant  under  natural  circum- 
stances.— The  battle  as  studied  in  pasture-land  or  meadow. — The 
grass-plots  at  Eothamsted — their  botanical  composition  and  the  way 
they  are  affected  by  manures  of  different  kinds. — The  Grasses,  their 
nature  and  differences ;  contrasts  between  nearly  allied  species. — 
The  Leguminosse. — The  Miscellaneous  weeds. — The  vegetation  and 
characteristics  of  the  continuously  unmanured  plot. — The  effects 
of  different  manures  and  of  different  combinations  of  manures  upon 
the  struggle.— Effects  of  disuse  of  manure,  and  of  the  substitution 
of  one  kind  for  another.— General  results. 

In  former  sections  mention  has  been  made  of  the  rela- 
tions which  the  living  plant  bears  to  the  heat,  light, 
moisture,  and  other  physical  conditions,  by  which  it  is 
surrounded.  These  conditions  are  sometimes  favorable, 
sometimes  prejudicial.  In  the  latter  case,  the  existence 
of  the  plant  becomes  a  prolonged  struggle  against  adverse 
influences.  To  a  certain  extent  it  is  always  so,  and  when 
the  difficulties  can  no  longer  be  counterbalanced  or  over- 
come, plants,  like  other  living  beings,  succumb  and  die. 
The  life  of  each  individual  then  may  be  described  as  a 
battle  against  circumstances. 


90  PLANT   LIEE   OJS  THE   FAKM. 

But  -apart  from  this  external  conflict  with  the  elements, 
plants  are  always  more  or  less  in  a  state  of  internecine 
war.  Plants  of  different  kinds  growing  wild  in  a  state  of 
nature  may  contend  one  with  another  for  root-hold,  soil- 
food,  and  for  space  to  expose  their  foliage  to  the  sun. 
Under  such  circumstances,  if  there  is  enough  for  all,  it 
may  be  that  the  severity  of  the  struggle  may  be  slight, 
owing  to  the  different  requirements  of  the  different 
plants,  but  even  then  the  stronger  of  the  two  will  eventu- 
ally prevail.  A  farmer,  however,  would  hardly  call  the 
preponderance  of  weeds  an  instance  of  the  survival  of 
the  fittest.  From  his  point  of  view  it  would  certainly 
not  be  so,  however  true  it  might  be  in  wild  nature. 
Plants  of  the  same  kind  growing  gregariously,  like  heaths 
on  a  moor,  have  the  same  requirements,  and  these  are 
supplied  in  about  equal  proportions  to  all  the  individual 
plants.  The  result  is  that  while  the  weak  ones  are 
crowded  out,  the  survivors  are  all  pretty  much  on  an 
equality  ;  but  once  the  balance  is  destroyed,  then  that 
which  is  the  stronger,  or  the  one  best  adapted  to  the  cir- 
cumstances under  which  it  is  placed,  will  survive. 

In  cultivation  we  have  illustrations  of  mixed  and  of 
gregarious  vegetation  in  the  sense  above  employed,  as 
well  as  of  alternate  vegetation  as  in  the  case  of  "rotation." 
In  the  case  of  the  cereals,  of  turnips,  of  potatoes,  and 
others,  we  have  instances  of  gregarious  vegetation 
induced,  indeed,  by  the  will  of  the  cultivator.  His 
object  is  to  secure  the  most  profitable  development  of 
one  particular  kind  of  plant,  wheat,  barley,  oats,  or  what 
not.  To  compass  this  end  he  grows  them  together, 
takes  means  by  appropriate  tillage,  and  by  the  removal 
of  competing  weeds,  to  enhance  the  conditions  most 
favorable  to  their  growth  and  to  minimize  the  effects  of 
those  that  are  injurious.  The  warfare  here  is  external 
as  regards  "weeds,"  it  is  internecine  between  individual 
plants  of  the  same  species  and  having  the  same  require- 


THE   BATTLE   OF   LIFE.  91 

ments.  As  the  competition  of  alien  plants  may  be  pre- 
vented by  weeding,  so  internecine  war  between  plant  and 
plant  of  the  same  kind  maybe  mitigated  by  the  adoption 
of  thin  seeding,  which  allows  each  individual  to  attain 
its  complete  development,  and  enables  it  to  avail  itself  to 
the  full  of  the  resources  at  its  disposal.  Unless  under 
exceptional  circumstances  and  for  some  special  purpose, 
it  is  more  profitable  so  to  grow  plants  as  to  diminish  the 
competition  between  individuals  by  affording  each  the  best 
possible  chance.  Otherwise,  the  strongest  or  best  adapted 
prevails,  indeed,  over  those  less  favorably  situate,  but 
there  is,  so  far  as  the  cultivator  is  concerned,  a  loss  of 
energy  and  a  waste  of  resource  in  the  case  of  the  beaten 
plants.  The  cultivator  requires  for  his  purpose  the 
largest  number  of  plants  of  good  average  quality  ;  nature 
favors  the  development  of  a  few  of  exceptional  power  of 
adaptation,  which  therefore  overcome  their  fellows,  but 
which  are  not  necessarily  the  best  for  the  farmer. 

The  Battle  in  the  Meadow, — The  battle  of  life  is  per- 
haps best  studied  in  mixed  pastures  where  a  great  variety 
of  plants  of  diiferent  families,  different  construction,  and 
different  requirements  are  grown  in  association.  In 
such  pastures  some  of  the  constituent  plants  are  valuable 
to  the  farmer,  as  some  of  the  grasses  and  most  of  the 
leguminous  plants  ;  others  are  relatively  useless  and  may 
be  positively  injurious.  The  behavior  of  the  different 
classes  of  plants  so  growing  in  association,  but  under 
varied  conditions  of  manuring,  for  a  large  number  of 
years,  has  been  made  the  subject  of  prolonged  and  elabo- 
rate study  at  Rothamsted.  A  few  of  the  leading  results 
may  here  be  mentioned  in  merest  outline  for  the  purpose 
of  illustrating  the  subject  of  this  chapter,  and  of  afford- 
ing matters  for  consideration  by  the  practical  cultivator. 

The  total  number  of  different  kinds  of  plants  that 
have  been  found  on  the  plots  is  eighty-nine,  of  which 


92  PLANT  LIFE   ON  THE  FARM. 

twenty  are  grasses,  ten  leguminous,  and  the  remainder, 
occurring  usually  in  smaller  proportions  and  belonging 
to  many  natural  orders,  are  conveniently  grouped  as 
"miscellaneous."  The  numbers  and  relative  proportions 
of  these,  as  noted  in  the  growing  herbage  or  recognized 
in  the  samples  taken  from  it,  differ  very  much  in  dif- 
ferent seasons,  and  more  especially  according  to  the 
nature  of  the  manure  employed. 

The  plants  vary  among  themselves,  the  grasses  having 
certain  characters  in  common,  the  leguminous  plants  dif- 
fering from  the  grasses,  and  both  more  or  less  from  the 
miscellaneous  plants,  the  members  of  which  latter  group 
differ  very  considerably  among  themselves.  The  varia- 
tions alluded  to  depends  of  course  on  the  varying  organi- 
zation, hereditary  endowments,  internal  structure,  habit, 
constitution,  and  mode  of  life  of  the  several  plants.  Some 
of  these  points  are  much  more  influenced  by  external 
conditions  of  soil  and  climate  than  others. 

The  Grasses.  *-Of  the  eighteen  grasses  which  commonly 
occur  on  the  plots  all  are  perennial  except  Bromus  mollis. 


*  In  the  text  the  Latin  names  of  the  plants  mentioned  are  employed 
as  more  precise  and  uniform  in  their  application,  not  varying  in  differ- 
ent localities,  and  being  in  universal  use  in  botanical  works  ;  but  as 
these  names  may  not  be  familiar  to  some  readers,  the  most  commonly 
adopted  English  names  are  here  supplied.  It  should  be  remembered 
that  only  the  more  important  of  the  pasture  plants  are  here  alluded  to. 
[The  common  names  most  in  use  in  the  United  States  are  added 
in  brackets.] 

GRASSES. 

Anthoxanthum  odoratum    -=  Sweet  vernal  grass. 

Alopecurus  pratensis  =  Meadow  fox  tail  grass, 

Phleum  pratense  =  Meadow  cat's-tail.  [Timothy.] 

Agrostis  vulgaris  =  Fiorin  grass.     [Red-top.] 

Aira  caespitosa  Tussack  or  hair  grass. 

Holcus  lanatus  =  Woolly  soft  grass. 

A  vena  pubescens  •=  Downy  oat-grass. 

"     elatior  •=•  False  oat-grass. 


THE  BATTLE  OF  LIFE. 


93 


They  occur  in  very  varying  proportions  on  the  different 
plots  according  to  the  season  and  according  to  the  nature 
of  the  manure  employed.  They  vary  somewhat  in  ro- 
bustness of  constitution  and  ability  to  withstand  frost  or 
drouth  ;  and  their  structural  characters  are,  generally 
speaking,  characteristically  different  from  those  of  other 
plants,  and  variable  as  between  species  and  species.  Some 
maintain  their  ground  or  even  increase  when  growing  in 
competition  or  association  with  their  fellows  ;  others — 
such  as  AntJioxantlmm  odoratum,  Festuca  ovina,  and 
Agrostis  vulgaris — can  only  hold  their  own  or  assert 
themselves  when  the  competition  exercised  by  their  asso- 
ciates is  relatively  weak,  and  succumb  under  the  opposite 
circumstances. 


Avena  flavescens  =  Yellow  oat-grass. 

Poa  pratensis  =  Meadow  grass.     [Blue  grass.] 

"  trivialis  —  Rough  stalked  meadow  grass. 

Briza  media  =  Quake-grass. 

Dactylis  glomerata  —  Cock' s-foot  grass.    [Orchard  G.] 

Cynosurus  cristatus  —  Crested  dog's-tail  grass. 

Festuca  ovina  —  Sheeps'  fescue. 

"       pratensis  —  Meadow  fescue. 

"        elatior  —  Tall  fescue. 

Bromus  mollis  =-  Soft  brome  grass. 

Lolium  perenne  —  Rye  grass. 

LEGUMINOS^E. 

Trifolium  repens  =  White  clover. 

"         pratense  —  Meadow  clover.     [Red  clover.] 

Lotus  corniculatus  =  Bird 's-foot  trefoil. 

Lathyrus  pratensis  =  Meadow  vetchling. 

WEEDS. 

Ranunculus-various  species=  Buttercups. 
Cerastium  triviale 

Conopodium  denudatum  = 

Centaurea  nigra  = 

Carduus  arvensis  = 

Bellis  perennis  = 

Achillea  Millefolium  — 


Taraxacum  officinale 
Plantago  lauceolata 
Rumex  Acetosa 


Mouse-ear  chickweed. 

Earth  nut. 

Knap-weed. 

Common  thistle.     [Canada  T.j 

Daisy. 

Milfoil.    [Yarrow.] 

Dandelion. 

Plantain  or  Rib  grass. 

Sorrel-dock. 


94  PLANT  LIFE  ON  THE  FARM. 

Th^  grasses,  both  in  number  of  species  and  in  relative 
and  actual  amount  of  produce,  exceed  the  plants  of  all 
other  orders.  The  lowest  produce  occurs  on  the  con- 
tinuously unmanured  plots  ;  the  highest  on  those  to 
which  a  highly  nitrogenous  manure,  such  as  ammonia 
salts  or  nitrate  of  soda,  is  continuously  applied  in  combi- 
nation with  earthy  and  alkaline  salts — especially  potash. 
But  while  the  total  gramineous  produce  is  thus  increased 
by  the  description  of  manure  just  mentioned,  the  num- 
ber of  species  of  grass  is  reduced.  On  the  unmanured 
plots,  on  the  average,  sixteen  different  sorts  of  grasses 
may  be  found,  each  contributing  a  fair  proportion  to  the 
total  herbage  ;  thirteen  only  are  found  on  the  highly 
ammoniated  plots,  and  of  these  only  a  very  few  contribute 
materially  to  the  crop,  the  remainder  being  present  in 
such  small  quantities  as  to  make  but  little  difference  in 
the  totals. 

The  principal  external  characteristics  which  favor  the 
growth  of  the  grasses  in  their  competition  with  other 
plants  are  their  dense  root-growth,  monopolizing  as  it 
were  all  the  soil  within  reach,  an$  affording  little  power 
to  the  roots  of  other  plants  to  penetrate  the  mass.  To 
an  extent  variable  in  different  species,  this  root-growth 
is  both  superficial  as  well  as  deep.  In  addition  to  this 
generally  ample  root  development,  many  of  the  species 
are  aided  in  the  struggle  by  their  stout  tufted  habit  and 
specially  by  their  power  of  producing  creeping  offshoots 
above  or  below  ground  which  insinuate  themselves  in 
between  other  plants  and  occupy  any  vacant  territory. 
No  doubt  internal  anatomical  differences  are  even  of 
greater  moment  than  these  external  characteristics,  but 
these  demand  minute  comparative  study  by  means  of  the 
microscope,  under  various  conditions,  and  at  different 
seasons,  and  constitute  a  branch  of  inquiry  at  present 
hardly  even  entered  upon. 

Although  grasses  as  a  whole  comport  themselves  in  a 


THE  BATTLE  OF  LIFE.  95 

particular  manner  distinct  from  that  of  the  other  tenants 
of  the  plot,  yet  it  is  found  that  individual  grasses,  and 
even  members  of  the  same  genus,  vary  very  much 
among  one  another. 

It  is  instructive  to  compare  the  different  tendencies  of 
the  two  most  generally  prevalent  grasses,  Festuca  ovina 
and  Agrostis  vulgaris.  As  to  structural  endowments 
they  would  seem  to  be  not  unfairly  matched,  but  the 
Festuca  is  conspicuously  worsted  on  the  plots  highly 
dressed  with  nitrogenous  manures,  while  the  Agrostis  is 
befriended  by  them,  and  its  vigor  and  tufted  habit  are 
increased.  Poa  trivialis  and  Holcus  lanatus  afford  con- 
trasts  of  a  similar  character,  the  Poa  being  largely  in- 
creased by  nitrate  of  soda,  while  the  Holcus  is  similarly 
acted  on  by  ammonia  salts.  Of  the  same  character  are 
the  differences  observable  between  Agrostis  vulgaris, 
which  is  influenced  by  ammonia  salts,  and  Holcus  lana- 
tus, Avena  pubescens,  and  Avena  flavescens,  which  are 
especially  acted  upon  by  nitrate  of  soda.  Very  marked 
contrasts  between  species  of  the  same  genus  also  occur, 
as  between  such  structurally  very  closely  related  plants 
as  Poa  trivialis,  and  P.  pratensis,  and  between  the 
three  species  of  Avena.  On  the  contrary,  Bromus  mollis 
and  Poa  trivialis  are  so  far  similar  that  nitrate  of  soda 
is  very  favorable  to  them  both.  Poa  pratensis  and 
Agrostis  vulgaris  concur  in  their  liking  for  ammonia 
with  mineral  salts,  while  they  manifest  opposite  tenden- 
cies with  regard  to  nitrate  of  soda ;  Poa  pratensis  not 
being  favored  by  it,  while  the  Agrostis  is  so  conspic- 
uously. 

These  are  only  a  few  of  the  remarkable  contrasts  and 
similarities  that  an  inspection  of  the  Rothamsted  records 
brings  out.  Perhaps  the  most  striking  point  in  this 
connection  is  the  opposite  tendency  manifested  by  differ- 
ent grasses  in  reference  to  the  action  of  ammonia  salts, 
and  of  nitrate  of  soda  respectively,  with  or  without 


96  PLANT  LIFE   ON  THE  FARM. 

mineral  manures  in  addition  in  each  case.  Doubtless, 
these  characteristics  are  to  be  correlated  with  differences 
of  organization  and  structure,  but  with  the  exception 
that  the  shallower  rooted  plants  are  often  favored  by 
ammonia  salts,  and  the  deeper  rooting  ones  by  the  more 
deeply  percolating  nitrate,  little  or  nothing  has  been  done 
in  definitely  associating  the  different  physiological  en- 
dowments above  referred  to,  with  corresponding  differ- 
ences of  internal  structure. 

The  LeguminoSft  form  a  group  of  plants  characterized, 
so  far  as  this  country  is  concerned,  by  the  presence  of 
"papilionaceous"  flowers  like  those  of  the  common  pea, 
by  their  leaves  being  compound,  i.  e.,  consisting  of  separ- 
able segments,  and  by  the  production  of  a  seed-pod, 
which,  when  ripe,  splits  into  two  valves  or  flaps  ;  this  is 
technically  called  a  "  legume."  By  these  characteristics, 
not  to  mention  others,  this  group  which  comprises  peas, 
beans,  clovers,  vetches,  sainfoin,  lucerne,  and  other  agri- 
cultural plants,  may  be  known.  Some,  such  as  peas 
and  beans  are  annual,  others  are  perennial,  and,  as  a  rule, 
their  habit  or  general  appearance  is  so  strikingly  dif- 
ferent from  that  of  the  grasses,  that  no  one  ever  con- 
founds them. 

Though  containing  a  larger  proportion  of  nitrogen  in 
their  composition  than  the  cereals,  they  are  not  specially 
benefited  by  nitrogenous  manures  as  the  grasses  are,  and 
this  fact,  observed  when  Leguminosas  are  grown  alone,  as 
in  the  bean  or  clover  field,  is  no  less  marked  than  it  is 
when  they  are  grown  in  association  as  in  pasture  land. 
At  Kothamsted,  the  largest  proportionate  quantities  of 
Leguminosae  occur  on  a  plot  to  which  mixed  mineral 
manure  with  potash  is  applied.  Seasonal  characteristics, 
even  when  favorable  to  these  plants,  do  not  suffice  to 
overcome  the  injurious  effects  of  some  manures,  as  during 
many  years  of  varying  character  as  to  climate,  they  have 


THE  BATTLE  OF  LIFE.  97 

been  practically  banished  from  the  ammonia  plots.  On 
the  whole  their  requirements  are  opposite  to  those  of  the 
grasses,  the  conditions  favoring  the  latter  not  being  any- 
thing like  so  propitious  to  the  leguminous  plants.  Thus 
the  effect  of  nitrogenous  manures  as  observed  on  the  ex- 
perimental plots  is  to  banish  or  reduce  more  or  less  com- 
pletely the  Leguminosae,  or  so  to  favor  the  growth  of  the 
grasses,  or  certain  of  them,  that  the  Leguminosae  are 
overpowered.  On  the  other  hand,  mineral  manures, 
which  are  not  by  themselves  very  beneficial  to  grasses, 
are  very  propitious  to  the  growth  of  leguminous  plants. 
Potash  is  especially  favorable  to  these  plants,  their  pre- 
dominance and  produce  is  always  enhanced  when  that 
substance  is  used  in  due  proportions  as  a  manure,  and 
always  diminished  when  it  is  omitted.  In  illustration,  it 
may  be  added,  that  on  the  plot  where  the  manurial  con- 
ditions are  most  favorable  to  Leguminosae,  the  weight 
per  cent  of  the  whole  crop  was  as  follows  : — Sixty-five 
per  cent  grasses,  twenty  per  cent  leguminous,  and  fifteen 
per  cent  miscellaneous.  The  per-centage  by  weight  on 
the  unmanured  plot  was,  sixty-eight  grasses,  nine  legu- 
minous, and  twenty-three  miscellaneous.  Taking  the 
other  extreme  where  a  large  quantity  of  nitrogenous 
manure  was  employed,  the  figures  are  ninety-five  per 
cent  grasses,  and  five  per  cent  miscellaneous,  the  Legu- 
minosae being  all  but  absent  (one  per  cent). 

Of  the  Leguminosae  of  pasture-land  LatJiyrus  praten- 
sis  seems  to  be  able  to  hold  its  own  under  adverse  condi- 
tions much  better  than  its  fellows,  the  clovers  or  the  Lo- 
tus. Its  long,  straggling  root,  and  scrambling  habit 
added  to  its  hardihood  may  be  the  source  of  these  advan- 
tages. 

Miscellaneous  Plants. — In  spite  of  the  large  number 
and  varied  habits  of  growth  of  the  miscellaneous  species 
found  on  the  plots,  their  importance  as  factors  in  the 
5 


98  PLANT  LIFE  OK  THE  FARM. 

struggle  is  less  than  that  of  the  grasses  and  of  the  legu- 
minous plants.  The  proportion  in  which  they  occur  on 
the  several  manured  plots  is  always  less  than  that  of  the 
grasses,  and  they  never  really  attain  any  very  great  de- 
gree of  prominence,  except  in  cases  where  from  seasonal 
or  manurial  causes  the  grasses  are  prevented  from  attain- 
ing their  full  development.  Those  species  which,  like 
Rumex  Acetosa,  have  a  powerful  underground  develop- 
ment, and  abundant  capacity  for  collecting  and  storing 
water,  etc.,  of  course  have  an  advantage  especially  when 
it  so  happens  that  they  can  avail  themselves  of  unoc- 
cupied territory,  which  they  seize  and  hold  with  great 
success  against  all  comers,  and  also  in  cases  where  the 
density  of  the  soil  is  such  as  to  offer  an  obstacle  to  the 
penetration  of  fibrous  roots.  But,  on  the  whole,  the 
dense  fibrous  net-work  of  roots  made  by  the  grasses, 
which  enables  them  to  avail  themselves  of  well  nigh 
every  particle  of  soil  within  their  reach,  is  a  more  valua- 
ble possession  than  is  the  more  robust  underground  root- 
stock  possessed  by  several  of  the  miscellaneous  plants. 
Most  of  the  species  occur  in  too  insignificant  amounts  to 
be  considered  as  anything  more  than  accidental  tenants, 
and  while  in  others  their  preponderance  depends  on  the 
relative  inferiority  of  the  growth  of  grasses,  there  are 
also  indications  that  some  of  them  are  favorably  affected 
by  certain  manures,  and  others  by  fertilizing  agents  of 
different  character.  But  on  the  whole,  these  indications 
observed  on  plants  growing  in  association  are  by  no  means 
so  marked  as  in  the  cases  of  the  grasses  and  the  Legu- 
minosse. 

Growth  of  Pasture  Plants  when  unaffected  by  manure 
of  any  kind. — The  changes  from  year  to  year  in  the  vege- 
tation of  a  plot  which  has  been  unmanured  for  many 
years  must  obviously  be  mainly  due  to  seasonal  influ- 
ences, and  progressive  exhaustion  of  the  soil,  while  those 


THE  BATTLE   OF  LIFE.  99 

•which  are  observed  in  the  manured  plots  are  as  obviously 
brought  about,  partly  by  the  manures  and  partly  by  cli- 
matal  changes.  The  produce  of  hay  at  Rothamsted, 
without  manure,  has  varied  from  eight  hundred  and 
ninety-six  pounds,  to  four  thousand  three  hundred  and 
sixty-eight  pounds,  the  average  for  twenty-five  years 
having  been,  as  before  stated,  two  thousand  five  hundred 
and  seventy-six  pounds  per  acre.  This  hay  is  made  up 
on  the  average  of  forty-nine  different  species  in  different 
proportions,  as  determined  by  rigid  comparative  scrutiny. 
Of  the  forty-nine  plants,  seventeen  are  grasses,  four  legu- 
minous plants,  and  the  remaining  twenty-eight  are  pas- 
ture weeds  of  various  orders,  and  roughly  classified  as 
miscellaneous  plants.  By  weight,  grasses  furnished  sixty- 
nine  .per  cent,  Leguminosae  eight,  and  miscellaneous 
plants  twenty-three  per  cent  of  the  total  produce. 

The  general  appearance  of  the  unmanured  plots  is  one 
of  even  growth,  with  no  special  luxuriance  of  any  par- 
ticular plant.  The  herbage  is  very  mixed,  the  crop 
scanty,  the  color  yellowish-green,  in  fact  a  sort  of  trades- 
union  equality  is  produced,  between  the  different  mem- 
bers of  the  community,  no  one  kind  being  specially 
favored.  Festuca  ovina  usually  predominates  among  the 
grasses.  Briza  media  is  more  abundant  on  these  plots 
than  on  most  others.  Among  the  leguminous  plants, 
Lotus  corniculatus  is  more  prevalent  than  LatJiyrus  pra- 
tensis,  as  is  usually  found  to  be  the  case  when  there  is 
soil  exhaustion  and  a  deficiency  of  potash.  The  miscel- 
laneous plants  are  generally  very  abundant,  such  as  the 
buttercups.  Plantago  lanceolata,  Centaurea  nigra,  Agri- 
monia  Eupatoria,  Scakiosa  arvensis,  Leontodon  hispidus, 
Prunella  vulgar  is,  Achillea  Millefolium,  Conopodium  de- 
nudatum,  Rumex  Acetosa,  Luzulacampestris,  and  Galium 
verum.  The  contrast  in  early  summer  between  the 
scanty  yellowish-green  herbage,  profusion  of  flowers  of 
the  various  weeds,  and  the  almost  total  absence  of  flowers 


100  PLANT  LIFE  Otf  THE  FARM; 

and  rich,  deep  blue-green  foliage  of  the  plants  in  the  ad- 
jacent ammonia  plot  is  very  striking. 

The  effects  of  manure  upon  the  struggle. — When  in 
a  long  series  of  years  the  effects  on  the  vegetation  of  a 
particular  plot  are  observed  to  be  uniform  in  their  nature, 
if  not  in  degree,  the  effects  are  obviously  attributable  to 
the  manure  employed,  and  the  fluctuations  are  as  clearly 
dependent  on  climatal  variations.  In  endeavoring  to 
give  an  idea  of  the  effect  of  different  manures  in  influen- 
cing the  nature  and  fierceness  of  the  struggle,  it  will  be 
convenient  to  allude  first  to  those  cases  in  which  no 
change  has  been  made  in  the  condition  of  manuring, 
mentioning  first  those  plots  in  which  comparatively 
simple  manures  are  employed,  and  afterwards  those  in 
which  a  more  complex  manure  is  employed. 

Mineral  manures  alone. — One  of  the  plots  at  Both- 
amsted  illustrates  the  effects  of  mineral  manures  consist- 
ing of  admixtures  of  various  earthy  and  alkaline  salts 
used  by  themselves,  without  the  admixture  of  nitroge- 
nous substances.  Speaking  generally,  it  is  there  observed 
that,  while  graminaceous  herbage  has,  with  much  fluctu- 
ation, slightly  increased,  the  proportionate  amount  of 
leguminous  plants,  as  compared  with  grasses,  has  on  the 
whole  been  largely  increased,  although  latterly  it  has 
shown  a  tendency  to  decline.  The  large  increase  is 
mainly  due  to  Lathyrus  pratensis,  which  prevails  over 
all  its  fellows.  The  grasses  which  hold  their  own  best 
are  Festuca  ovina,  Agrostis  vulgaris,  and  Holcus  lana- 
tus.  Achillea  Millefolium  has  increased  considerably, 
Conopodium  denudatum  and  Rumex  Acetosa,  have  usually 
been  abundant.  This  description  of  manure  seems  un- 
favorable to  most  of  the  weeds  of  pasture-land  other  than 
the  above  mentioned.  The  crop  is  generally  moderate, 
with  an  even  and  early  ripening,  and  a  marked  tendency 


THE  BATTLE   OF   LIFE". 


to  stemmy  as  distinguished  from  leafy  growth,  the  color 
of  the  foliage  being  of  a  light,  yellowish-green. 

On  the  wheat  plots,  it  has  been  shown  that  purely 
mineral  manures  scarcely  increase  the  yield  at  all,  though 
they  are  beneficial  to  the  leguminous  crops.  These  ex- 
periments confirm  Boussingault's  assertion  that  alkaline 
or  earthy  salts,  although  indispensable  to  plants,  never- 
theless, exercise  no  action  unless  combined  with  matters 
capable  of  furnishing  nitrogen. 

Superphosphate  of  lime  only.  —  The  scanty  and  stemmy 
produce  on  the  plot,  to  which  this  substance  is  applied, 
has  been  but  little  greater  than  that  on  the  unmanured 
plots.  The  grasses  and  miscellaneous  plants  have  been 
slightly  increased,  the  Leguminosae  diminished.  There 
has  been  a  great  admixture  of  species,  but  little  luxuri- 
ance of  any.  Holcus  lanatus,  Avena  flavescens,  Poa 
trivialis,  Lolium  perenne,  and  Festuca  ovina  have  been 
among  the  most  prominent  grasses,  while  the  freer-grow- 
ing Dactylis  does  not  apparently  find  so  much  sub- 
sistence as  it  requires.  LatJiyrus  pratensis  among  the 
leguminous  plants,  and  Rumex  Acetosa  and  AcMllea 
Millefolium  among  the  weeds,  have  but  slightly  benefited, 
others  yielding  even  less  than  without  manure.  Bous- 
singault's  observations,  already  quoted  under  the  head  of 
mineral  manures,  apply  equally  here.  The  great  French 
chemist  found,  as  in  the  Rothamsted  experiments,  that 
superphosphate,  uncombined  with  substances  capable  of 
yielding  ammonia,  produced  little  or  no  effect  on  vege- 
tation. Boehm's  experiments,  however,  go  to  show  that 
young  plants  raised  in  distilled  water,  die  before  the  nu- 
tritious matter  stored  up  in  the  seed,  or  in  the  seed- 
leaves  is  exhausted,  but  if  lime  be  added,  especially  in 
the  form  of  ulinate,  before  this  point  is  reached,  the 
seedlings  resume  their  healthy  appearance,  the  develop- 
ment of  the  radicle,  according  to  Deherain,  being  par- 
ticularly favored  by  this  substance.  (See  p.  18), 


LIFE   O^s"  THE  FARM. 

Superphosphate  has  been  proved  to  be  of  little  or  no 
use  to  other  crops  grown  separately,  except  in  the  case  of 
turnips,  where  about  eight  tons  per  acre  have  been  pro- 
duced by  the  use  of  superphosphate  ;  the  produce  with- 
out manure  at  all,  being  one  to  two  tons  per  acre. 

Ammonia  Alone* — The  average  produce  with  ammonia 
salts  alone  has  not  been  very  much  greater  than  that  on 
the  unmanured  plots.  The  principal  differences  are  in 
the  grasses,  which  have  diminished  as  to  number  of  spe- 
cies, but  largely  increased  in  proportionate  amount  to 
the  other  plants.  Agrostis  vulgaris,  and  especially  Fes- 
tuca  ovina,  both  poor  grasses,  are  so  greatly  favored, 
that  they  constitute  the  bulk  of  the  crop,  while  other 
better  grasses  have  diminished,  even  Dactylis  glomerata 
not  being  by  any  means  prominent.  Ammonia  salts  are 
not  propitious  to  any  of  the  Leguminosae,  but  Lotus  cor- 
niculatus  has  had  slightly  the  advantage  over  the  others. 
Among  the  miscellaneous  plants  which,  like  the  Legu- 
minosse,  are  well-nigh  banished,  Rumex  Acetosa  had  the 
advantage  ;  Conopodium  denudatum  also  seems  to  have 
benefited  in  some  seasons.  The  crop  is  generally  moder- 
ate, of  a  rich,  green  color,  and  late  in  ripening,  with 
much  foliage,  and  relatively  little  tendency  to  flower. 

Nitrate  of  Soda  alone. — The  general  results  of  the  ap- 
plication of  this  salt  have  been  an  increased  proportion 
of  grasses,  particularly  of  Festuca  ovina,  Alopecurus  pra- 
tensis,  Holcus  lanatus  and  Poa  trivialis,  P.  pratensis 
being  scarcely  represented.  There  is  in  general  not 
much  tendency  to  form  stem  among  the  grasses.  Legu- 
minosse  exist  in  but  scanty  proportions,  but  among  them 
Lotus  corniculatus  seems  to  have  slightly  the  advantage. 
In  the  case  of  beans  grown  separately,  nitrate  of  soda, 
unlike  ammonia,  is  found  to  be  beneficial.  Among  mis- 
cellaneous plants,  Rumex  Acetosa  and  Gentaurea  nigra, 


THE   BATTLE  OF  LIFE.  103 

are  specially  noteworthy  for  their  abundance  ;  Ranunculi 
are  also  in  fair  quantity.  Plantago  has  diminished,  but 
the  most  remarkable  feature  is  the  enormous  quantity  of 
Cerastium  triviale  produced  under  the  influence  of  this 
manure. 

Nitrate  of  soda  gives  a  late-ripening  dark  green  crop, 
more  leafy  than  stemmy  in  character,  but  nevertheless 
showing  a  greater  disposition  to  form  stem  than  in  the 
case  of  plants  treated  with  ammonia. 

Superphosphate  and  Ammonia.— The  effects  produced 
by  this  combination,  have  corresponded  to  those  which 
are  met  with  in  other  plots  to  which  ammonia  is  added, 
viz.,  increased  produce,  chiefly  of  graminaceous  herbage, 
greatly  diminished  leguminous  herbage,  and  relative  ab- 
sence of  miscellaneous  plants.  Festuca  ovina  has  enor- 
mously increased,  and,  to  a  less  extent,  the  hardy  creep- 
ing Agrostis  vulgar  is.  On  the  other  hand  Antlioxan- 
tJium  odoratum,  Holcus  lanatus,  and  Avena  pubescens, 
•have  decreased.  The  crop  is  usually  later  in  ripening 
than  in  the  case  of  that  to  which  the  superphosphate 
alone  is  applied,  and  with  more  dark  green  leaf  and  less 
stem,  characters  which  indicate  the  presence  of  ammonia. 

Minerals  and  Ammonia. — In  all  the  plots  to  which 
ammonia  and  minerals  have  been  continuously  applied, 
the  produce  is  large,  the  per-centage  and  weight  of 
grasses  large,  those  of  leguminous  plants  small  or  nil, 
and  those  of  miscellaneous  weeds  also  small.  These  effects 
are  greater  and  more  observable,  the  larger  the  quantity 
of  ammonia,  though  the  effects  are  by  no  means  doubled 
in  intensity,  when  the  quantity  of  ammonia  is  doubled. 
The  average  produce  has  been  larger  than  that  of  the 
other  plots.  The  number  of  species  has  diminished, 
especially  in  the  case  of  miscellaneous  plants.  Where  the 
ammonia  was  in  relatively  slight  proportions,  Festuca 


104  PLAXT   LIFE   ON  THE   FARM. 

ovina>  Agrostis  vulgaris,  Avena  elatior,  Holcus  lanatus 
and  Poa  pratensis,  are  noted  to  have  been  predominant, 
Poa  trivialis,  on  the  contrary,  being  practically  banished. 
The  two  first-named  plants  owe  their  predominance  not 
exclusively  to  the  manure,  for  they  thrive  luxuriantly 
under  many  other  conditions.  A  similar  remark  applies 
to  Rumex  Acetosa.  On  those  plots  where  the  quantity 
of  ammonia  salts  was  doubled,  Dactylis  glomerata  for 
some  years  was  in  enormous  preponderance,  Agrostis  vul- 
garis, Holcus  lanatus,  Alopecurus  pratensis  and  Avena 
elatior  have  been  also  in  large  quantities.  Briza  media. 
Cynosurus  cristatus,  Lolium  perenne,  Bromus  mollis,  all 
poor  grasses,  except  Lolium,  have  been  discouraged  by 
the  ammonia.  Poa  trivialis  also  has  greatly  diminished 
in  proportion  to  the  quantity  of  P.  pratensis. 

Among  the  miscellaneous  plants,  Ranunculacese,  like 
the  Leguminosse,  have  been  practically  banished.  Um- 
belliferae  have  been  almost  expelled,  Composite  largely 
diminished,  Labiates  greatly  reduced ;  Plantago  lanceo- 
lata  is  unrepresented,  and  even  Rumex  Acetosa  consider- 
ably diminished.  As  these  or  corresponding  effects  are 
generally  observed  where  ammonia  forms  part  of  the  ma- 
nure employed,  and  as  they  are  enhanced  when  the 
quantity  is  increased  (though  not  in  direct  proportion), 
it  would  seem  that  ammonia  must  be  actually  prejudicial 
to  some  plants.  It  is  probable,  however,  that  the  dimin- 
ished proportion  of  these  plants  is  more  often  due  to  the 
increased  luxuriance  of  the  stronger-growing  grasses  than 
to  the  directly  prejudicial  effects  of  the  manures  on  the 
other  plants. 

It  is  generally  observed,  that  on  the  ammonia  plots 
the  plants  show  a  great  tendency  to  form  leaves,  and 
when  mineral  manures  are  added,  the  period  of  ripening 
is  hastened,  and  its  degree  enhanced.  A  combination  of 
mineral  and  ammonia  salts,  where  the  latter  are  not  in 
excessive  proportion,  is  beneficial  to  almost  all  crops,  as 


THE   BATTLE   OF   LIFE.  105 

to  Cereals,  Crucifers  (turnips),  Chenopods  (beet,  man- 
gels), Solanums  (potatoes),  etc. 

Minerals  and  Nitrate, — The  produce  in  those  cases 
where  this  combination  is  used  is  generally  large,  ripens 
early,  is  of  a  dark  green  color,  with  abundant  foliage 
and  relatively  little  stem.  The  per-centage  of  grasses 
has  been  large,  that  of  Leguminosae  very  small,  and  that 
of  miscellaneous  plants  on  the  whole  greatly  reduced, 
effects  which,  in  general  terms,  are  very  similar  to  those 
observed  on  the  mineral  and  ammonia  plots. 

The  mineral  and  nitrate  appears  to  have  encouraged 
the  growth  of  Poa  trivialis,  Bromus  mollis,  and  latterly 
of  Alopecurus  pratensis,  while  leguminous  and  miscel- 
laneous plants  have  been  discouraged.  The  following 
grasses  are  discouraged  by  nitrate :  Briza  media,  Cyno- 
surus  cristatus,  Poa  pratensis.  Leguminosae  in  general 
and  Umbelliferae  and  some  Composites  are  also  discour- 
aged. 

Cerastium  triviale,  Plantago  lanceolata,  Galium  verum, 
Centaur ea  nigra,  and  Ranunculus,  are  slightly  favored 
by  the  nitrate. 

The  combination  of  minerals  and  ammonia  favors  the 
growth  of  Poa  pratensis,  Agrostis  vulgarls,  Festuca 
ovina,  etc.,  more  than  does  the  admixture  of  mineral 
and  nitrate.  On  the  other  hand,  the  following  species, 
among  others,  are  more  benefited  by  mineral  and  nitrate 
than  by  mineral  and  ammonia  :  Poa  trivialis,  Dactylis 
glomerata,  Bromus  mollis,  and  Lolium  perenne,  etc. 

In  some  seasons,  especially  in  years  of  drouth,  (1870), 
Bromus  mollis  was  extremely  prevalent,  its  deep  roots 
giving  it  an  advantage  over  others. 

Effects  of  change  of  Manure,— The  object  sought  at 
Rothamsted  in  changing  the  conditions  of  manuring  has 
been  to  ascertain  definitely  to  what  particular  ingredient 


106  PLANT  LIFE   OK  THE  FARM. 

in  a  mixed  manure  a  particular  effect  is  due,  and  to  ob- 
tain confirmation  of  the  results  obtained  by  other 
methods.  By  adding  or  by  withholding  a  particular  salt, 
as  the  case  may  be,  an  answer  to  the  question  proposed 
may  be  obtained.  In  the  following  paragraphs  the  effects 
of  the  disuse  of  certain  manures,  and  then  of  the  substi- 
tution of  one  kind  for  another,  will  be  very  briefly  allud- 
ed to. 

Disuse  of  Manure  of  any  Kind.— On  a  plot  to  which 
farm-yard  manure  was  applied  it  was  observed  that  while 
the  produce  was  largely  increased,  more  so  indeed  than 
under  almost  any  other  circumstances,  the  per-centage 
of  grasses  and  of  some  of  the  miscellaneous  weeds  was 
increased,  while  the  leguminous  herbage  was  diminished. 
On  discontinuing  the  dung  the  vegetation  of  the  plot 
was  observed  gradually  but  uniformily  to  approximate 
to  that  of  the  unmanured  plot,  the  number  of  species 
increasing  without  any  marked  preponderance  of  any, 
and  good  grasses  like  Poa  trivialis  giving  place  to  poorer 
ones,  such  as  Festuca  ovina. 

Disuse  of  Farm-yard  Manure. — Another  plot  which 
originally  received  a  combination  of  dung  and  ammonia, 
has  been  treated  since  1864  with  a  small  dose  of  ammonia 
salts  only.  Here  the  grasses  and  the  Leguminosse  are 
diminishing  as  to  numbers,  but  the  luxuriance  of  those 
species  that  remain  is  increased.  The  miscellaneous 
weeds,  especially  Rumex  Acetosa,  and  the  Composites, 
are  decreasing,  Ranunculacece  decline,  and  even  more 
markedly  so  the  Umbelliferce  and  Plantago  lanceolata, 
the  latter  plant  being  very  sensitive  to  ammonia. 

Disuse  of  Potash, — The  first  effect  noticeable  after 
the  disuse  of  potash  was  a  diminished  produce  of  grasses. 
Leguminosae  have  also  continuously  and  strikingly  deT 


THE  BATTLE   OF   LIFE.  10? 

creased,  while  miscellaneous  plants,  especially  Achillea 
Millefolium  and  Rumex  Acetosa,  have  increased. 

The  increase  of  Festuca  ovina  is  probably  not  so  much 
due  to  any  favoring  effect  of  the  manure  as  to  the  en- 
feeblement  of  its  competitors.  AnthoxantJium  odoratum 
has  increased,  but  almost  all  the  other  grasses  have 
diminished.  Ranunculacece,  Composite,  especially  Achil- 
lea, have  increased  since  the  disuse  of  potash.  Umbel- 
lifers,  Plant  ago  lanceolata,  and  Rumex  Acetosa  have 
decreased. 

On  the  plot  where  ammonia  is  added  to  mineral  ma- 
nures, but  where  potash  is  omitted,  the  grasses  show  a 
large  per-centage  from  the  effect  of  the  ammonia ;  the 
leguminous  plants  are  almost  banished,  owing  to  the 
combination  of  unfavorable  circumstances,  i.  e.y  the 
presence  of  ammonia  and  the  absence  of  potash.  Kanun- 
culaceae  are  diminishing,  as  are  also  Umbelliferae,  Com- 
posites, Plantago  lanceolata,  and  Rumex  Acetosa. 

As  a  general  rule,  it  is  recognized  that  the  growth  of 
plants  is  checked  if  the  quantity  of  potash  be  reduced 
bevond  a  certain  limit.  Deherain  has  recently  shown 
that  in  the  case  of  the  buckwheat,  starch  is  not  gener- 
ated from  chlorophyll  unless  potash  be  present.  If  potash 
be  added,  then  starch  begins  to  be  formed.  Neither 
sodium  nor  lithium  can  usefully  replace  potash,  though 
extremely  little  is  known  as  to  the  functions  of  the  lat- 
ter. Salts  of  potash  and  magnesia  have  also  a  general 
tendency  to  augment  the  weight  of  leaves,  while  chloride 
of  sodium  favors  the  development  of  stem. 

Substitution  of  Mixed  Mineral  Manures  for  Ammo- 
nia.— The  consequences  of  the  disuse  of  ammonia,  and 
the  employment  in  its  stead  of  mineral  manures,  are 
shown  in  diminished  produce,  the  grasses  having  been 
diminished,  the  leguminous  and  the  miscellaneous  plants 
increasing  in  number  and  proportion.  Festuca  ovina. 


108  PLANT  LIFE   OH  THE  FARM. 

has  been  the  most  prominent  grass,  while  Laihyrus  pra- 
tensis  has  manifested  considerable  increase,  and  Rumex 
Acetosa  has  been  the  most  prominent  among  the  miscel- 
laneous plants. 

The  greatest  change  after  some  years  was,  however, 
not  in  the  distribution  of  the  species,  but  rather  in  the 
character  of  their  development  and  their  increased 
tendency  to  form  stem  and  seed. 

Summary. — From  the  foregoing  details  it  is  manifest 
that  the  plants  found  on  the  several  plots  vary  very 
greatly  in  number,  in  character,  and  in  degree  of  de- 
velopment, according  to  the  nature  of  the  manurial 
agent  employed,  the  ever  varying  character  of  the  sea- 
sons, and  the  association  or  hostile  competition  of  their 
neighbors.  These  several  conditions  rarely,  if  indeed 
ever,  act  singly,  but  almost  always  in  combination.  Cir- 
cumstances are  never  exactly  twice  alike  ;  a  condition  of 
absolute  equilibrium  is  never  attained.  The  nearest  ap- 
proach to  it  has  been  reached  in  the  case  of  the  unma- 
nured  plot  on  the  one  hand,  and  of  the  very  highly  ma- 
nured plots  on  the  other,  but  these,  like  the  others,  are 
influenced  by  climatal  changes  occurring  now  at  one 
stage  of  growth,  now  at  another.  And  even  when  a 
comparative  state  of  equilibrium  is  attained,  very  slight 
causes,  even  such  as  may  be  roughly  called  accidental,  as 
the  injuries  inflicted  by  insects,  or  parasitic  fungi,  suffice 
to  disturb  the  balance  and  bring  about  a  different  arrange- 
ment and  proportion  of  species,  and  a  corresponding 
change  in  the  development  of  individual  plants. 

As  to  the  action  of  manures  on  the  plants,  it  is  com- 
paratively rarely  that  they  are  employed  in  such  quanti- 
ties as  to  be  absolutely  destructive  or  poisonous.  In  most 
cases — even  when  a  particular  manure  is  proved  to  be 
more  or  less  directly  injurious  to  particular  plants — the 
indirect  harm  accruing  from  the  beneficial  action  of  the 


PBACTICAL  IKFEEE^CES.  109 

substance  on  some  other  plant  or  plants,  growing  in  as- 
sociation with  them,  is  greater  than  the  direct  mischief. 
The  manures  act  very  differently  on  different  plants,  and 
vary  in  their  action,  even  in  the  same  species,  according 
to  the  time  and  stage  of  growth  at  which  they  are  em- 
ployed. Some  encourage  the  growth  and  development 
of  their  cellular  tissues,  at  the  expense  of  the  woody  and 
fibrous  constituents,  others  favor  the  consolidation  of 
the  tissues,  hasten  the  flowering  period,  and  bring  about 
an  increased  production  of  seed.  But  any  change  that 
may  be  induced  is  of  a  physiological  kind,  affecting  the 
development  of  the  individual,  not  the  character  of  the 
species.  By  no  combination  of  manurial  elements  is  it 
possible  to  bring  about  that  kind  of  change  which  a 
naturalist  would  consider  specific. 


CHAPTER  VIII. 
PRACTICAL  INFERENCES. 

Objects  for  which  plants  are  cultivated,  and  the  means  of  promoting 
them. — Plants  cultivated  for  their  roots — for  their  foliage — for  their 
fibre — for  their  seeds. — Farming  operations  as  aids  to  propitious  cli- 
matal  influences  and  as  counteracting  the  evil  effects  of  injurious 
ones. — Drainage. — Tillage. — Manures.— Change  and  variety  of  crop- 
ping.— Rotation. — Improvement  of  cultivated  plants. — Selection, — 
Change  of  seed.— Cross  breeding. 

Having  in  the  preceding  chapters  given  an  outline  of 
the  life-history  of  the  plant,  the  machinery  by  which  it 
is  carried  on,  the  manner  in  which  that  machinery  fulfils 
its  purpose,  and  the  contest  and  competition  in  which 
living  plants  are  always  engaged,  it  may  be  well  to  indi- 
cate some  of  the  points  in  which  the  history  so  outlined 
affects  the  practice  of  agriculture.  Of  course,  were 


110  PLANT   LIFE    ON   THE    FARM. 

science  perfect,  which  it  is  very  far  from  being,  and  were 
practice  uniformly  intelligent  and  uninfluenced  by  mere 
routine  or  accidental  circumstances,  it  would  be  found 
that  no  single  detail  of  the  plant's  history  was  unimpor- 
tant to  the  cultivator.  As  it  is,  owing  to  deficient 
knowledge  on  both  sides,  much  of  what  the  student 
learns  in  the  laboratory  has  no  application  in  the  field, 
and  much  of  what  the  farmer  does  on  the  land  is  without 
significance  to  the  student. 

It  is  the  object  of  the  series  of  Handbooks,  of  which 
this  is  one,  to  remedy  this  state  of  things,  and  to  bring 
the  two  classes  of  workers  more  into  accord,  so  as  to  en- 
sure a  greater  amount  of  co-operation  beneficial  to  both 
parties.  The  special  value  to  the  cultivator  of  scientific 
knowledge  will  probably  be  found  in  the  power  it  gives 
him  of  availing  himself  of  new  resources  and  of  adapting 
himself  to  altered  conditions — no  light  matter  in  the 
present  state  of  agriculture. 

In  endeavoring  to  turn  to  account  some  of  the  lessons 
which  vegetable  physiology  is  able  to  teach,  we  have  in 
the  first  instance  to  consider  what  is  the  special  object 
with  which  any  particular  crop  is  cultivated,  because,  as 
has  been  shown,  the  conditions  suitable,  say  for  the 
growth  of  wheat,  are  not  those  most  fitting  for  the  pro- 
duction of  forage  or  of  root-crops.  Then  it  must  be 
repeated  that  we  grow  plants  for  our  own  benefit,  and 
only  indirectly  for  the  advantage  of  the  plant  itself.  It 
may  be  that  the  objects  for  which  we  cultivate  a  particu- 
lar plant  are  of  such  a  nature  as  to  be  best  compassed  by 
means  most  favorable  to  the  general  health  and  welfare 
of  the  plant,  as  in  the  case  of  cereals,  or  it  may  be  that 
we  grow  the  plant  for  one  particular  product,  to  secure 
which  we  endeavor  to  promote  disproportionate  leaf- 
growth  or  root-  growth,  as  the  case  may  be,  at  the  ex- 
pense of  the  other  organs  of  the  plant,  and  so  bring 
about  what  is  really  an  unnatural  and  morbid  condition. 


PRACTICAL   INFERENCES.  Ill 

In  offering  a  few  general  considerations  on  these  sub- 
jects, in  addition  to  the  numerous  incidental  references 
in  other  pages,  it  may  here  be  convenient  to  arrange 
plants  according  as  they  are  cultivated  for  their  roots, 
inclusive  of  root-like  organs,  for  their  stems,  and  for 
their  leaves,  fruits,  or  seeds  ;  omitting  all  those  special 
details .  pertaining  to  what  we  may  term  the  individual 
constitution  of  plants. 

Plants  Cnltivated  for  their  Roots,  etc, — Under  this 
head  are  included  such  crops  as  turnips,  kohl  rabi, 
potatoes,  beet-root,  mangels,  and  onions.  In  all  of  these 
the  cellular  tissue  largely  preponderates  over  the  fibrous. 
The  cells  are  filled  With  water  and  with  various  substances, 
such  as  starch  and  other  secretions.  In  the  economy 
of  the  plant  these  secretions  are  manufactured  in  one 
season,  stored  in  the  cells,  and  used  up  in  the  next  season 
for  the  production  of  leaves,  flowers,  and  seeds.  The 
work  of  the  leaves  then  of  these  plants  differs  to  some 
extent  according  to  season  ;  those  of  the  first  year  work 
to  build  up  the  plant  and  to  store  up  the  secretions  in 
the  "  roots"  or  tubers,  while  the  office  of  those  produced 
in  the  succeeding  year  is  more  particularly  to  form  and 
nourish  the  flower,  fruit,  and  seed,  and  to  secure  the  ac- 
cumulation of  nutritive  matter  in  the  seed.  Unless  the 
farmer  requires  the  plants  to  seed,  he  uses  up  the  roots 
for  his  own  purposes  before  any  demand  is  made  upon 
the  plant  for  flower  and  fruit  building. 

Speaking  generally,  the  indications  furnished  by  the 
nature  of  the  plants,  point  to  the  necessity  or  desirability 
of  a  light,  rich,  friable  soil  for  their  culture,  one  which 
will  permit  of  ready  root  range,  and  which,  while  sup- 
plying ample  food,  shall  not  harbor  stagnant  water. 
Rapid  growth  and  vigorous  leaf-action  are  also  indicated, 
as,  when  these  are  secured,  the  cellular  portions  required 
grow  in  proportion  faster  and  more  freely  than  the 


112  PLANT   LIFE   ON  THE   FARM. 

fibrous  portions,  and  the  requisite  secretions  are  stored 
the  more  readily  in  the  roots.  To  ensure  this  rapid 
growth,  more  essential  in  an  annual  crop  like  potatoes 
than  in  those  whose  growth  occupies  part  of  two  seasons, 
a  warm  aspect  and  a  well  drained  soil  are  essential,  while 
to  ensure  the  formation  of  the  secretions  which  render 
the  plant  valuable,  free  exposure  to  light  is  also  requisite. 
Thus,  hoeing  and  weeding  owe  their  good  effects  not 
only  to  the  removal  of  useless  plants  occupying  space 
that  might  more  profitably  be  employed,  but  they  secure 
to  the  crop  freedom  from  the  shade  of  the  weeds,  and 
promote  the  access  of  light  to  the  foliage  and  of  air  to 
the  roots.  The  excessive  action  of  the  vegetative  organs 
checks,  to  a  varying  extent,  the  development  of  the 
fruiting  organs  ;  indeed,  the  object  of  culture  is  to  keep 
the  plant  growing  and  to  prevent  its  flowering.  If  the 
seed  of  such  plants  is  sown  too  early,  growth  is  apt  to  be 
slow,  and  woody  fibre  is  produced  where  succulent  cells 
would  be  preferable,  and,  moreover,  the  tendency  to 
produce  flowers  is  enhanced  by  the  high  summer  tem- 
perature which  follows.  If  sown  late,  the  growth  of  the 
vegetative  organs  is,  for  a  time,  rapid,  because  the  soil  is 
warmer  and  the  sky  lighter,  while  the  tendency  to  form 
fibre  and  flower  is  checked. 

The  formation  of  subterranean  tubers  may  be  taken  as 
an  indication  that  the  plant  prefers  a  period  of  rest. 
The  rest  is,  indeed,  not  absolute,  but  relative  ;  and  while 
little  external  change  may  be  visible,  it  is  probable,  and 
in  some  cases  certain,  that  considerable  chemical  changes 
go  on  during  the  period  of  apparent  inaction.  Under 
natural  circumstances  the  rest  is  secured,  either  by  the 
occurrence  of  heat  and  drouth,  or  of  a  very  low  tempera- 
ture, the  action  of  light  being,  in  either  case,  excluded. 
These  facts  supply  hints  as  to  the  proper  mode  of  storing 
and  pitting  potatoes  and  roots.  Moisture,  light,  and  air 
should  be  excluded,  the  temperature  kept  as  low  as  pos- 


PRACTICAL  INFERENCES.  113 

sible,  short  of  frost,  and  what  is  of  even  more  impor- 
tance, kept  as  uniform  as  possible.  By  such  means  the 
roots  may  be  kept  dormant,  and  the  waste  to  the  farmer, 
which  would  occur  from  the  unseasonable  growth  of  the 
plant  using  up  the  food  intended  for  his  cattle  or  sheep, 
obviated. 

Plants  Cultivated  for  their  Foliage,— Among  these 
are  the  various  green  crops  and  forage  plants,  cabbages, 
mustard,  clovers,  sainfoin,  lucerne,  vetches  and  pasture 
grasses.  Apart  from  the  special  requirements  of  each 
particular  'plant,  such  as  the  special  influence  of  nitro- 
genous manures  in  promoting  leaf -growth  among  grasses, 
and  of  mineral  manures  in  fostering  the  leafy  develop- 
ment of  leguminous  plants,  and  the  special  demands 
made  by  particular  circumstances,  the  object,  in  all  cases, 
is  to  ensure  a  rapid,  abundant  and  nutritious  leaf -growth. 
In  some  cases  where  otherwise  too  great  acridity  might 
be  produced,  it  is  desirable  to  secure  shade  to  the  leaves, 
and  thus  prevent  the  formation  of  the  objectionable 
matters.  Thus,  in  the  case  of  cabbages  the  grower  pre- 
fers those  which  "heart"  well,  i.  e.,  those  in  which  the 
leaves  are  tightly  packed  one  over  the  other,  and  do  not 
readily  separate  ;  and  this  tendency  is  increased  by  con- 
stantly selecting  for  seed  those  varieties  in  which  this 
peculiarity  is  seen  to  be  most  marked.  At  other  times 
the  production  of  objectionable  secretions  is  obviated  by 
the  process  of  "  earthing  up,"  as  in* the  case  of  celery,  or 
by  tying  up  the  leaves  as  in  lettuces. 

The  development  of  leaves  is  of  course  largely  depen- 
dent on  the  well-being  of  the  roots,  so  that,  in  a  general 
way,  all  those  conditions  of  soil  which  are  propitious 
to  the  development  of  roots  are  so  also  to  that  of  leaves. 

The  requirements  of  particular  plants  are  so  varied, 
according  to  their  affinity  and  the  very  diverse  modifica- 
tions of  form  and  structure  presented  by  their  roots.,  that 


114  PLANT  LIFE   OK  THE  PARM. 

only  generalities  can  here  be  alluded  to.  The  cultivator 
must  observe  for  himself  whether  the  plants  he  wishes  to 
grow  are  naturally  shallow  or  deep-rooted  ;  whether  the 
roots  break  up  into  a  dense  leash  of  fine  fibres  encom- 
passing and  traversing  in  all  directions  the  soil  within  a 
certain  limited  area;  or  whether,  as  in  the  case  of 
lucerne,  the  "root"  consists  of  a  long,  thick  under- 
ground stem,  capable  of  extending  itself  for  many  feet, 
and  giving  off,  within  a  small  extent,  only  a  compara- 
tively small  number  of  fibres.  The  different  forms  of 
roots  previously  alluded  to  may  be  looked  on  as  adapta- 
tions to  different .  conditions  of  the  soil,  especially  in 
relation  to  water,  and  the  choice  of  site  and  mode  of 
tillage  must  be  governed  by  circumstances.  Leaf-de- 
velopment is  thus  consequent  on  root-growth  •  but,  in 
addition,  an  adequate  supply  of  moisture  and  heat  and 
full  exposure  to  light  are  demanded.  The  adjustment 
of  these  agencies  is  rarely  under  the  control  of  the  far- 
mer to  anything  like  the  same  extent  that  it  is  in  the 
case  of  the  gardener.  The  gradener  can  often  contrive, 
for  instance,  by  appropriate  modifications  of  treatment, 
to  keep  his  plants  in  a  growing  condition,  and  to  prevent 
them  from  "  bolting  "  into  flower,  whereas  the  agricul- 
turist is  much  more  the  slave  of  circumstances.  Drouth 
and  heat  check  his  crops  before  their  growth  is  complete, 
and  induce  premature  development  of  fibre,  of  flower,  or 
of  seed.  Excessive  moisture  and  superfluity  of  rich  food 
will  cause  the  crops  to  become  too  rank  in  their  growth, 
to  develop  immature  succulent  tissue,  comparatively 
devoid  of  the  nutritious  secretions  in  which  their  value 
consists,  and  will  check  the  development  of  flowers. 

The  observant  eye  of  the  farmer  soon  detects  the  un- 
healthy state  of  the  crops  by  the  color  of  the  leaves.  If, 
from  any  cause,  root-action  is  deficient,  or  sun-heat  and 
sunlight  are  lacking,  the  chlorophyll  is  not  formed  in 
sufficient  amount,  or  is  imperfectly  developed,  and  the 


PRACTICAL  INFERENCES.  115 

consequence  is  a  yellow  languid  look  about  the  leaves, 
betokening  starvation.  On  the  other  hand,  excessive 
size  and  succulence  and  too  deep  a  green  hue  indicate  an 
excess  of  stimulant  nitrogenous  food  and  a  deficiency 
both  of  mineral  food  and  carbon  assimilation,  in  con- 
sequence of  which  growth  is  arrested.  In  such  cases  the 
amount  of  root-food  taken  up  is  out  of  proportion  to  the 
.amount  of  leaf -food.  If  the  season  could  be  prolonged 
so  as  to  ensure  a  longer  duration  of  leaf -action,  the 
balance  might  be  adjusted,  but  this  is  rarely  the  case. 
Appearances  in  such  cases  are  apt  to  be  misleading  to 
the  inexperienced.  There  is  an  appearance  of  luxuriant 
vegetation  with  which  the  intrinsic  nutritive  value  of  the 
crop  is  not  in  accordance. 

Plants  grown  for  Fibre, — Apart  from  timber  trees, 
hemp  and  flax  are  the  only  two  crops  generally  grown 
on  any  large  scale  for  their  fibre,  although  the  develop- 
ment of  the  straw  of  cereals  is  dependent  on  the  same 
conditions.  By  hereditary  transmission  these  plants 
manifest  a  tendency  to  produce  fibre  in  greater  propor- 
tionate amount  than  cellular  tissue.  Heat  and  light  are 
specially  requisite  to  ensure  the  formation  and  proper 
development  of  the  fibre.  Both  are  naturally  plants  of 
hotter,  drier,  more  luminous  climates  than  ours  ;  never- 
theless, if  they  can  be  grown  rapidily  they  yield  fibre, 
although  the  secretions  of  oil,  in  the  seed  of  the  flax 
(linseed),  and  of  narcotic  resin  in  the  case  of  the  hemp, 
are  not  produced  in  a  relatively  sunless  atmosphere. 

The  formation  of  timber  is,  in  general  terms,  the  for- 
mation of  fibre  on  a  large  scale.  Eoot  development, 
according  to  the  special  nature  of  the  tree,  of  course 
conduces  to  the  formation  and  proper  development  of 
leaves.  Trees,  from  their  root-range  being  wider  than 
that  possessed  by  herbaceous  plants,  can  collect  food  over 
a  larger  area,  and  thus  can  extract  nourishment  from  a 


116  PLANT  LIFE    0$  THE   FARM. 

comparatively  poor  soil  which,  would  starve  other  plants 
with  less  capacity  for  food  collection  and  less  duration  of 
working  life.  The  larger  the  leaf -surf  ace,  and  the  more 
fully  and  thoroughly  it  can  be  exposed  to  light,  the 
greater  quantity  of  timber  and  the  sounder  its  quality. 
It  may  be  requisite  for  certain  purposes  to  have  straight 
unbranched  spars,  and,  in  such  cases,  leaf-action  is  im- 
peded and  side-growth  is  arrested  by  thick  plantations 
and  neglect  of  thinning  ;  but  the  actual  amount  of  tim- 
ber is  necessarily  less  in  such  trees  than  in  others  of  the 
same  age  allowed  to  develope  freely  on  all  sides.  Coppice 
wood  is  also  grown  for  a  special  purpose,  which  practically 
justifies  that  mutilation  which,  like  most  pruning  opera- 
tions, is  of  course  at  variance  with  natural  growth.  In 
the  annual  growth  of  timber  it  may  readily  be  seen  that 
the  greatest  activity  of  growth,  i.e.,  formation  of  new 
tissues,  takes  place  in  the  first  few  weeks  after  vegetation 
commences.  After  that,  the  period  of  maturation  or 
consolidation  commences.  A  moist,  warm,  growing 
period  is,  therefore,  most  propitious.  The  process  of 
maturation  requires  for  its  fulfilment  greater  heat,  less 
moisture,  and  more  intense  light,  and  in  proportion  to 
the  degree  in  which  these  requirements  are  satisfied,  are 
the  amount  and  quality  of  the  timber.  Should  a  wet, 
sunless  autumn  be  succeeded  by  an  early  frost,  when 
maturation  is  imperfect  or  incomplete,  the  results  to  the 
young  growth,  that  is,  to  the  crop  of  timber  for  the  year, 
are  correspondingly  disastrous.  The  effect  of  mineral 
manures,  especially  potash,  in  promoting  the  develop- 
ment of  the  fibrous  tissue  in  grasses,  has  been  already 
alluded  to  ;  the  largest  absolute  amount  of  straw  being 
yielded  by  a  mixed  mineral  manure  with  a  large  supply 
of  ammonia. 

Plants  grown  for  their  seed. — The  remarks  just  made 
as  to  the  development   of  timber  as  a  consequence  of 


PRACTICAL  ItfFEREtfCES.  117 

maturation,  apply  mutatis  mutandis  to  the  development 
of  the  fruits  and  seeds.  The  farmer,  however,  especially 
requires  for  the  culture  of  seed-plants  which  are  grown 
as  annuals,  a  rapid,  uniform,  vigorous  growth,  followed 
by  a  steady  progress  towards  maturity,  a  condition 
favored  by  the  gradual  cessation  or  modification  of  leaf- 
work,  and  as  simultaneous  a  ripening  of  all  the  fruits  or 
seeds  on  the  plant  as  possible.  The  mode  of  develop- 
ment of  the  inflorescence  generally  considered  of  mere 
technical  or  botanical  interest,  is  here  obviously  a  matter 
of  practical  importance,  for  plants  in  which  the  flowers 
and  fruits  ripen  in  succession  are  obviously  less  suited 
for  the  farmer's  purposes  than  those  in  which  the  flowers 
of  a  particular  inflorescence  open  approximately  at  the 
same  time — as  they  do  in  the  cereals.  To  ensure  the 
production  and  good  condition  of  the  crop,  as  in  the  case 
of  cereals,  of  beans,  peas,  buckwheat,  etc.,  the  first 
requisites  to  success  are,  of  course,  those  which  promote 
the  proper  germination  of  the  seed,  and  then  those  which 
favor  the  due  development  of  the  root  according  to  the 
nature  of  the  plant.  To  a  considerable  extent  the  farmer 
is  here  master  of  the  situation,  and  by  drainage  and 
tillage  appropriate  to  the  varied  nature  of  the  soil  and 
the  character  of  the  season,  he  can  promote  and  favor 
both  germination  and  root-growth.  Over  leaf-actioa, 
independent  of  that  which  is  the  direct  outcome  of  root- 
growth,  he  has  less  control,  as  he  is  at  the  mercy  of  the 
seasons.  If  cold,  wet,  growing  periods  are  followed  by 
dull,  cloudy,  maturing  seasons,  the  crop  must  be  deficient 
in  quantity  or  quality,  or  both.  The  reasons  for  this 
deficiency  have  been  repeatedly  given.  The  farmer  is 
not  so  able  as  the  gardener  to  overcome  these  defects,  but 
he  is  at  least  able  in  a  measure  to  evade  them  by  cultivat- 
ing not  only  a  variety  of  different  crops,  but  numerous 
varieties  of  the  same  crop,  some  of  which  are  sure  to 
prove  better  adapted  to  sustain  themselves  under  hostile 


118  PLANT  LIFE  ON  TflE  FARM. 

conditions  than  others.  Thus  spring  wheat,  barley,  of 
oats,  may  be  made  in  a  degree  to  supply  the  deficiencies 
of  the  autumn  sown  wheat,  and  tares,  beans,  peas, 
carrots,  etc.,  etc.,  employed  to  compensate  for  the  failure 
of  other  crops. 

Manures. — By  the  judicious  use  of  suitable  manures 
at  the  right  time,  the  farmer  is  also  enabled  in  some  de- 
gree to  provide  for  and  counteract  the  effects  of  unpro- 
pitious  seasons.  Farm-yard  manure,  for  instance,  not 
only  increases  the  quantity  of  grain  and  of  straw,  but 
greatly  improves  the  quality  of  the  grain,  as  measured  in 
pounds  per  bushel ;  and  the  same  holds  good  of  a  mixed 
mineral  and  nitrogenous  manure. 

The  time  when  nitrogenous  manures  can  be  most 
beneficially  applied  is  a  matter  of  great  consequence, 
Messrs.  Lawes  and  Gilbert  having  proved  that  the 
nitrogen  carried  off  the  land  in  the  drainage  water,  is 
much  greater  when  the  manure  is  applied  in  the  autumn 
than  when  used  in  spring.  Another  illustration  of  the 
use  of  manures  of  an  opposite  character  to  that  just 
cited,  is  afforded  by  the  use  of  common  salt  (sodium 
chloride)  to  check  rank  growth  with  its  tendency  to  pro- 
duce straw  rather  than  grain. 

The  varying  effects  of  season,  according  to  the  nature 
of  the  manure  employed,  suggest  also  that  a  variety  of 
manures  should  be  used.  In  the  Rothamsted  experi- 
ments, it  has  been  shown  that  the  seasons  which  proved 
most  propitious  to  the  unmanured  crops,  and  to  those  to 
which  only  mineral  manures  were  applied,  were  not 
equally  so  for  the  crops  to  which  nitrogenous  manures 
were  applied;  hence,  says  Sir  J.  B.  Lawes/'  the  best  season 
for  land  in  low  condition  is  not  the  best  for  land  in  high 
condition." 

The  varying  effects  of  manure  may  be  illustrated  by  a 
few  figures  taken  from-  the  Rothamsted  "memoranda"  : 


PKACTICAL  USTFEKEtfCES.  119 

thus,  in  the  case  of  wheat,  the  average  produce  per  acre 
over  thirty  years,  was  about  thirteen  bushels  on  the 
unmanured  plots,  as  against  thirty-six  on  highly  manured 
plots  (mineral  and  ammonia  salts,  and  mineral  and 
nitrate  respectively),  some  plots  also  producing  the  largest 
quantities  of  straw,  the  nitrate  producing  rather  more 
than  the  ammonia.  The  quality  of  the  produce  of  wheat 
as  measured  in  pounds  per  bushel  is  not  so  different, 
that  on  the  unmanured  plots  being  usually  nearly  equal 
to  that  of  the  highly  manured  plots.  From  this  point  of 
view,  farm-yard  manure  proved  more  beneficial  than  the 
artificial  nitrogenous  and  mineral  manure  yielding  the 
largest  quantity  of  grain.  The  corresponding  figures  in 
the  case  of  barley,  are  seventeen  and  forty-nine  ;  the 
highest  produce  was  with  nitrate  and.  minerals,  but  the 
largest  amount  of  straw  was  yielded  with  a  manure  con- 
taming  a  large  proportion  of  nitrate  of  soda  with 
minerals.  Of  hay,  the  average  produce  under  like  cir- 
cumstances over  twenty  years,  was  two  thousand  three 
hundred  and  fifty  two  pounds  on  the  unmanured,  and 
six  thousand  nine  hundred  and  forty-four  pounds  on 
highly  manured  plots  (mineral  and  ammonia.) 

In  like  manner,  turnips  varied  from  one  or  two  tons  per 
acre  without  manure  to  eight  tons  with  superphosphate, 
and  nine  to  twelve  tons  with  superphosphate  combined 
with  nitrogenous  manure,  such  as  ammonia  or  rape-cake. 
Sugar  beet  produced,  when  unmanured,  from  seven  to 
eight  tons  per  acre  in  the  earlier,  to  five  tons  in  the  later 
years,  but  eighteen  tons  with  farm-yard  manure  ;  nitro- 
genous manures  increased  the  yield  largely,  but  super- 
phosphate was  of  no  use  to  the  beet  and  mangel.  With 
mangel,  the  produce  on  the  unmanured  plot  was  from 
one  to  six  tons  per  acre  (average  4.6  tons),  as  compared 
with  nineteen  tons  with  farm-yard  manure  (or  on  the 
average  fourteen  tons).  Potatoes  varied  from  about  half 
a  ton  on  the  unmanured,  or  about  two  tons  on  the 


120  PLAHT  LIFE  OK  TSE  FARM. 

average,  to  four  to  five  tons  with  farm-yard  manure, 
and  to  six  to  seven  tons  with  mixed  mineral  and  am- 
monia. The  tendency  to  disease,  however,  increases  with 
the  higher  manuring,  in  larger  proportion  than  does  the 
produce. 

The  data  of  science  on  the  effect  of  manures  must, 
however,  only  be  taken  as  indications  by  the  practical 
farmer,  who  must  be  guided  by  financial  considerations 
and  local  conditions,  in  determining  what  it  is  best  for 
him  to  do  under  particular  circumstances  at  any  given 
time. 

An  interesting  circumstance  may  here  be  mentioned, 
viz  :  that  many  of  our  cultivated  plants,  such  as  cab- 
bages and  mangold  wurzel,  have  sprung  from  wild  plants 
growing  by  the  sea,  and  are  hence  especially  benefited  by 
the  use  of  salt  as  a  manure.  Onions,  the  growth  of 
which  is  also  favored  by  salt,  probably  originated  from  a 
wild  stock  growing  in  salt  desert  regions. 

Fallow, — The  good  effects  of  this  may  be  judged  from 
the  results  of  some  Eothamsted  experiments,  in  which 
the  produce  of  wheat  is  recorded,  after  bare  fallow,  com- 
pared with  that  of  wheat  grown  continuously  on  the 
same  soil,  without  the  intervention  of  fallow,  and  equally 
without  manure.  Under  such  circumstances,  the  aver- 
age produce  for  twenty -five  years  after  fallow  has  been 
eighteen  bushels  per  acre,  as  contrasted  with  an  average 
of  twelve  bushels  where  the  wheat  has  been  grown  con- 
tinuously. The  weight  per  bushel  was  the  same  in  both 
cases.  The  average  quantity  of  straw  after  fallow  was 
one  thousand  seven  hundred  and  eighty-six  pounds,  as 
contrasted  with  one  thousand  two  hundred  and  twenty- 
one  pounds,  where  the  crop  was  grown  continuously. 

Rotation. — The  practice  of  rotation  of  crops  is  amply 
borne  out  by  what  occurs  in  nature  and  by  chemical  ex- 


PRACTICAL  ItfFEREKCES.  121 

periments,  although  not  in  the  manner  that  might  at 
first  have  been  supposed.  Leguminous  plants,  such  as 
clover,  beans,  vetches,  though  containing  so  much  nitro- 
gen in  their  composition,  are  not  only  not  specially  bene- 
fited by  nitrogenous  manures,  but  they  absolutely  leave 
the  land  richer  in  nitrogen  than  it  was  before  (Lawes 
and  Gilbert),  and  thus  prepare  it  for  the  growth  of  grain 
crops,  which,  though  chiefly  starch -producing,  'are  yet 
specially  benefited  by  nitrogenous  manures. 

In  growing  beans  and  wheat  alternately  at  Kotham- 
sted,  it  was  found  that  eight  crops  of  wheat  grown  al- 
ternately with  beans  supplied  nearly  as  much  produce 
(grain),  and  nearly  as  much  nitrogen  in  that  produce  as 
were  furnished  by  sixteen  crops  of  wheat  grown  without 
manure.  Here,  then,  the  manure  supplied  to  the  beans 
not  only  favored  those  plants,  but  left  a  residue  in  an 
available  form  for  the  wheat. 

Botanically,  the  good  effects  of  rotation  are  dependent 
on  the  variations  in  the  mode  of  growth  and  in  the  in- 
ternal structure  of  roots,  which  allow  of  different  layers 
of  soil  being  utilized  for  plant-food,  while  the  specially 
different  requirements  of  different  classes  of  plants  obvi- 
ate the  exhaustion  of  any  one  ingredient,  and  give  time 
for  the  accumulation  of  fresh  supplies. 

Improvement  of  Cultivated  Plants.— This  has  already 
been  alluded  to,  but  its  importance  justifies  repetition, 
the  more  so  as  to  a  considerable  extent  it  is  a  matter  that 
the  farmer  can  do  for  himself.  A  series  of  small  experi- 
mental plots  might  well  be  instituted  on  every  farm. 
The  first  and  perhaps  most  general  use  to  which  such 
trial  grounds  should  be  put,  would  be  to  test  the  quality 
of  purchased  seed,  and  ascertain  what  proportion  might 
be  expected  to  grow  under  different  conditions.  Other 
experiments  should  be  devoted  to  the  purpose  of  ascer- 
taining what  particular  varieties  are  likely  to  do  best  in 
6 


PLANT  LIFE  OK  THE  FAKM. 

particular  places.  The  investigator  who  sets  to  work  to 
produce  really  improved  varieties,  has  a  more  difficult 
task  before  him,  owing  to  the  number  of  excellent  varie- 
ties already  in  existence.  The  consequence  of  this  is 
that  much  labor  and  patience  must  be  expended  before 
any  real  improvement  on  what  is  already  in  existence  can 
be  expected,  although  there  is  the  chance  that  a  real  ad- 
vance may  be  made  almost  at  once.  The  large  capital 
employed  by  the  seed-houses  in  raising  and  introducing 
improved  varieties — real  or  so-called — is,  at  least,  a  testi- 
mony that  the  practice  is  pecuniarily  profitable  to  the 
trader,  and  forms  therefore  a  resource  which  the  agricul- 
turist might  develop  for  himself  to  a  larger  extent  than 
he  does.  He  would  reap  the  advantage  on  his  own  farm, 
even  if  he  lacked  the  capital  and  enterprise  requisite  to 
conduct  a  commercial  speculation  away  from  it. 

Selection. — The  improvement  of  the  races  of  cultivated 
plants,  as  previously  alluded  to,  is  indicated  by  Nature 
herself.  In  a  wheat  field  or  bean  crop  no  two  plants  are 
exactly  alike  :  one  is  more  robust  than  another,  one 
tillers  more  than  the  rest,  the  ears  of  one  are  plumper 
and  fuller,  this  one  grows  earlier  or  later  in  spring,  is 
therefore  hardier  or  more  tender,  as  the  case  may  be. 
The  careful  observer  notes  these  points,  and  instead  of 
passing  them  over,  endeavors  to  turn  them  to  account  by 
selecting  the  plant  which  shows  a  tendency  to  vary, 
taking  seed  from  it  and  growing  that  seed  another  season. 
A  certain  proportion  of  the  offspring  is  pretty  sure  to 
reproduce  the  desired  qualities,  probably  even  to  mani- 
fest them  in  an  enhanced  degree.  This  leads  to  further 
and  repeated  selection,  till,  at  length,  a  new  race  or 
variety  is  established.  When  it  is  remembered  whab 
vast  results  have  accrued  from  the  improvement  of  wheat 
and  turnips  by  selection  of  this  kind,  it  seems  remarka- 
ble that  further  efforts  are  not  made  in  this  direction, 


PRACTICAL  INFERENCES. 

and  especially  by  selecting  forms  which  observation 
would  show  are  specially  suited  to  a  particular  locality. 
Thus  Rivett's  red  wheat  produced  at  Rothamsted,  on  an 
average  of  eight  years,  fifty-three  bushels  of  grain  per 
acre,  while  Hallett's  original  red,  grown  under  the  same 
conditions,  yielded  only  thirty-six  bushels. 

Change  of  Seed. — This  is  a  practice  followed  with  ad- 
vantage by  both  gardener  and  farmer,  for  it  is  found  that 
the  crop  is  improved  when  seed  even  of  the  same  variety 
is  obtained  from  a  distance  where  it  has  been  grown 
under  different  conditions  of  soil  and  climate.  In  such 
cases  it  is  better,  where  possible,  to  select  seed  grown  on 
a  poorer  soil  and  under  more  unfavorable  conditions  than 
obtain  where  it  is  proposed  to  sow.  The  increased  vigor 
and  degree  of  fertility  resulting  from  this  process  have 
been  commented  on  by  Darwin. 

Cross  Breeding  by  means  of  artificial  fertilization 
is  an  operation  not  so  much  within  the  power  of  an 
ordinary  agriculturist,  owing  to  the  delicacy  of  manipu- 
lation and  length  of  time  required  to  ensure  results  worth 
having.  Such  experiments  would  be  better  accomplished 
in  the  laboratory  or  experimental  garden  of  the  professed 
physiologist.  The  experiments  carried  out  by  Andrew 
Knight,  Maund,  and  Sheriff,  in  the  case  of  wheat  and 
oats  are,  however,  encouraging.  "When  undertaken  for 
practical  purposes,  it  is  specially  desirable  that  mere  hap- 
hazard crosses  should  not  be  encouraged,  much  less  made 
purposely,  but  that  a  definite  object  should  be  pursued 
in  a  definite  manner.  The  experimenter  should  set  him- 
self to  work  to  endeavor  to  produce  an  earlier,  a  hardier, 
a  more  prolific  variety,  as  the  case  may  be,  selecting  for 
his  purpose  such  varieties  to  breed  from  as  he  has  ascer- 
tained by  experience  to  be  of  such  a  nature  as  likely  to 
yield  promising  results.  It  is  not  possible  to  give  detailed 


PLANT  LIFE   ON  THE  FAEM. 

instructions  here  as  to  the  way  in  which  cross-breeding 
may  be  carried  out ;  it  is  difficult  with  cereals,  less  so 
with  leguminous  plants,  easiest  with  the  cabbage  tribe. 
Indeed,  as  growers  know  to  their  cost,  it  is  difficult  to 
keep  the  races  or  strains  of  the  cabbage-tribe  pure  and 
uncontaminated,  owing  to  the  facility  with  which  the 
flowers  are  fertilized  by  insects  which  bring  the  pollen 
from  the  flower  of  some  other  variety.  Too  high  breed- 
ing, however,  often  entails  a  delicacy  of  constitution  or 
a  defective  productiveness  which  may  be  overcome  by  a 
fresh  cross  with  a  stronger  strain. 


CHAPTER  IX. 
DECAY  AND  DEATH. 

Change,  waste  and  repair.— Disturbance  of  the  balance.— Death  of  the 
protoplasm. — Causes  of  death.— Natural  death. — How  plants  die: 
impaired  nutrition,  starvation,  suffocation,  structural  injury  and 
paralysis.— Death  beginning  at  the  root.— Death  beginning  at  the 
leaf. 

Decay  and  Death* — Life  is  one  continual  series  of 
changes — 

"By  ceaseless  action  all  that  is  subsists." 

The  result  of  these  changes  is  gain  or  loss,  waste  or 
repair,  now  one,  now  the  other ;  or  occasionally  (and 
indeed  generally)  both  simultaneously.  While  a  proper 
balance  and  equitable  adjustment  between  gain  and  loss 
exists,  the  plant  lives  and  is  healthy.  Directly  the  bal- 
ance is  disturbed  the  plant  may  live  indeed,  but  it  be- 
comes unhealthy;  and  if  the  disturbance  continue — if 
waste  overtake  repair — if  nutrition  be  persistently  im- 
paired, still  more  if  it  be  arrested,  the  plant  inevitably 


DECAY   A^D   DEATH.  125 

dies.  This  is  that  gradual  and  slow  but  sure  inarch  of 
destiny  which  comes  sooner  or  later  to  all  living  things 
at  their  appointed  time.  That  time  comes  when  the 
tissues  are — from  that  degeneration  of  their  substance 
which  may  be  a  morbid  process  resulting  from  injury, 
or  which  may  be  merely  the  necessary  result  of  the 
growth  and  maturation  of  the  plant,  or  from  the  failure 
of  supplies — no  longer  able  to  carry  on  their  life-work. 
The  period  in  question  varies  as  to  its  occurrence.  A 
wheat  plant  uses  up  its  life  within  a  few  months,  an  oak 
tree  within  a  few  centuries,  and  there  is  every  inter- 
mediate period. 

But,  in  addition  to  changes  which  are  the  result  of  an 
inevitable  march  of  events,  death  in  plants  sometimes 
comes  suddenly  from  violence,  life  action  is  arrested  in 
its  full  flow  and  tide,  and  by  much  the  same  essential 
causes  as  those  which  extinguish  the  life  of  animals. 
The  death  of  plants  is  the  death  of  the  protoplasm.  Pre- 
vent the  access  of  oxygen  to  the  living  cell,  and  the 
movements  of  the  protoplasm  will  be  arrested  and  ulti- 
mately cease  altogether.  The  properties  and  functions 
of  protoplasm  have  already  been  explained.  It  is  their 
destruction  and  their  cessation  which  constitute  death. 
But  the  death  of  a  part  is  not  necessarily  the  death  of 
the  whole,  and  the  individual  cells  of  plants  are,  as  a 
rule,  much  more  independent  one  of  the  other  than  are 
the  individual  cells  of  an  animal.  A  root  or  a  leaf,  or  a 
mass  of  roots,  and  a  number  of  leaves  may  be  injured,  or 
even  killed,  and  the  plant  will  still  live  on,  because  there 
are  more  left  behind  uninjured ;  and  these,  relatively 
speaking,  do  not  suffer  from  the  damage  done  to  their 
fellows.  A  tree  may  be  stripped  of  its  leaves  and  may 
still  live,  because  there  are  cells  which  are  uninjured,  and 
which  will  do  their  parts  towards  compensating  the 
injury.  A  felled  tree  by  the  roadside  will  often  be  seen 
pushing  up  new  shoots  in  a  manner  that  would  be  im- 


126  PLANT   LIFE   ON  THE  FARM. 

possible  in  the  case  of  an  analogous  injury  done  to  one 
of  the  higher  animals.  The  lower  the  organism,  the  less 
special  in  its  conformation  and  construction,  the  more 
independent  are  its  constituent  cells.  The  higher  the 
organism,  and  the  more  specialized  its  structure,  the 
more  dependent  one  upon  another  are  the  structural  ele- 
ments of  which  it  is  compounded. 

Natural  death  may  be  described  as  an  exhaustidn  of 
the  protoplasm — its  water  evaporates  or  is  drafted  else- 
where ;  and  so  with  its  soluble  or  liquid  contents — the 
insoluble  and  the  useless  remain  behind.  We  see  this  in 
the  case  of  the  leaves  every  autumn  ;  their  protoplasm 
dries  up,  their  chlorophyll  degenerates  and  disappears ; 
they  are  emptied  of  starch  and  other  matters,  which  are 
conveyed  to  some  other  part  of  the  tree  to  be  stored  up 
for  future  use  by  the  new  growths  in  the  following  sea- 
son, until  at  length  nothing  is  left  but  a  framework  of 
dry  cellulose,  a  quantity  of  mineral  or  earthy  matter,  and 
such  material  as  could  not  be  dissolved  or  transported. 
In  other  organs  the  continuous  maturing  process  at 
length  results  in  the  blocking  up  of  the  cells  and  tubes 
by  continued  deposit  in  the  interior.  Osmosis  can  no 
longer  go  on  between  them,  for  their  altered  structure 
prevents  it,  and  in  consequence  the  protoplasm  disap- 
pears. Just  as  in  human  beings,  the  minute  blood-ves- 
sels get  "  bony  "  or  otherwise  deteriorated  in  structure, 
so  do  the  cells  and  fibres  of  plants  become  unfit  to  carry 
on  the  processes  of  life. 

For  the  purposes  of  the  cultivator,  it  is  very  desirable 
that  he  give  an  eye  to  the  way  in  which  plants  die  and  to 
the  causes  in  which  induce  death.  The  subject  may  be 
looked  at  from  various  points  of  view.  From  the  struc- 
tural point  of  view,  death  may  begin  in  the  cells  of  the 
root,  in  those  of  the  stem,  in  those  of  the  intermediate 
"collar,"  or  in  those  of  the  leaves,  and  the  appearances 
presented  will  be  found  to  differ  correspondingly. 


,        DECAY   AKD   DEATH.  127 

From  a  physiological  point  of  view  death  may  result 
from  starvation  or  from  suffocation  ;  the  process  in  each 
case  may  be  partial  and  gradual  or  immediate  and  com- 
plete. Sudden  death,  or  death  by  violence,  results  from 
the  injuries  inflicted  by  too  high  or  too  low  a  tempera- 
ture, electric  shocks,  sunstroke,  strong  corrosives,  and 
the  like.  These  destroy  life  by  disorganizing  the  pro- 
toplasm, breaking  up  the  tissues,  and  arresting  the 
natural  movements,  and  cause  death  by  destroying  the 
machinery  or  paralyzing  its  action.  The  gradual  effects 
produced  by  such  injurious  agencies  as  noxious  vapors 
from  kilns  or  factories,  or  as  insects,  or  parasitic  fungi 
are  the  same  as  those  produced  by  starvation  or  suffoca- 
tion. In  the  neighborhood  of  towns  it  may  happen  that 
the  relative  absence  of  oxygen,  or,  what  comes  to  the 
same  thing,  the  inability  to  use  what  there  is,  may  con- 
duce to  the  death  of  plants  quite  as  much  as  the  direct 
injury  caused  by  noxious  vapors.  A  perusal  of  the  fore- 
going -chapters  as  to  the  food  and  growth  of  plants  will 
suffice  to  show  why  plants  die  ;  and  a  consideration  of 
their  life-history  as  here  set  forth  will  show  how  the 
cause  that  may  kill  at  one  stage  of  active  growth  may  be 
all  but  harmless  at  another  stage  of  growth  (see  p.  64). 

Death  beginning  at  the  Root. — When  death  begins  at 
the  root,  the  supply  of  water  and  of  the  air  and  food  de- 
rived from  the  soil  is  cut  off,  and  the  plant  ultimately 
perishes  of  starvation.  Death  at  the  root  may  result 
from  injury  inflicted  by  small  parasitic  worms,  insects, 
rats,  or  other  creatures — from  unsuitable  conditions  of 
soil,  too  much  or  too  little  water,  deficient  drainage, 
deficient  aeration,  or  from  the  presence  of  really  poison- 
ous ingredients.  If  the  cause  is  widespread,  so  as  to  in- 
volve a  majority  or  the  whole  of  the  roots,  the  conse- 
quences are  proportionately  serious ;  if  only  a  few  are  af- 
fected; the  plant  may  not  be  visibly  or  materially  injured, 


PLAKT  LIFE   ON  THE  FAKM. 

The  effects  will  be  first  and  most  especially  olrvious  at 
the  point  of  injury,  and  at  the  growing  points,  where  the 
life-functions  happen  to  be  going  on  most  vigorously  at 
the  time.  Thus,  if  the  young  shoots  and  young  leaves 
are  in  full  activity  at  the  time  when  root-mischief  occurs, 
they  will  the  soonest  show  the  effect  of  cutting  off  sup- 
plies— they  will  wither  and  droop.  If  the  process  is  slow 
and  gradual,  the  leaves  will  become  emptied  of  their 
contents,  their  chlorophyll  will  change  color,  the  plant 
will  assume  a  sickly  yellow  look  very  characteristic  to 
the  practiced  eye.  The  older  portions  of  the  plant,  with 
their  reserve  stores  of  water  and  food,  may  not  immedi- 
ately suffer ;  and  it  is  from  them  that  the  materials 
requisite  for  any  effort  at  repair  and  reorganization  must, 
if  it  be  possible,  be  made.  Thus  a  plant  may  grow  for 
some  time  after  injury,  and  then  suddenly  flag  because 
its  reserve  supplies  are  at  length  exhausted.  It  follows 
from  this  that  death  from  starvation  as  a  consequence 
of  root-mischief  is  not  generally  a  sudden,  but  more  often 
a  gradual  process,  the  length  of  time  of  course  varying 
according  to  the  nature  of  the  mischief,  and  specially 
according  to  the  nature  and  condition  of  the  plant. 

Death  beginning  at  the  Leaf,— This  may  be  appre- 
ciated from  what  has  been  before  said  as  to  the  functions 
of  the  leaf.  The  leaf  is  an  organ  of  nutrition,  of  respira- 
tion, and  transpiration;  if  its  functions  are  sufficiently  in- 
terfered with,  death  will  result,  either  from  inanition  or 
from  suffocation,  or  from  both  combined.  The  power  of 
resistance  that  a  leaf  has  may  be  inferred  from  its 
structure.  A  thick,  fleshy  leaf,  with  layer  after  layer  of 
chlorophyll-containing  cells,  with  abundance  of  pores 
and  a  thick  skin,  is  obviously  better  able  to  resist  in- 
jurious agencies  than  a  thin  leaf  whose  delicate  texture 
speedily  withers  and  falls  a  prey  to  adverse  circum- 
stances. 


DECAY  AND   DEATH.  129 

The  fall  of  the  leaf  in  the  case  of  deciduous  trees  has 
heen  already  alluded  to.  It  is  only  requisite  here  to  say 
that,  under  the  circumstances,  <tbafc  it  is  a  natural 
process  ;  and  it  is  one  that  is  provided  for  from  the 
beginning.  From  a  very  early  stage  in  the  development 
of  the  leaf,  a  special  layer  of  cells  has  been  gradually 
forming  at  the  base  of  the  leaf -stalk  at  right  angles  to 
the  others,  which  ultimately  cuts  off  the  dying  and  dead 
leaf -cells  from  the  living  tissues  of  the  bark,  much  as 
the  "  drop  scene"  of  a  theatre  separates  the  body  of  the 
house  from  the  stage  at  the  close  of  the  performance. 
The  leaf  is  emptied  of  its  contents,  and  further  supplies 
from  below  are  eventually  stopped  off  by  the  intervention 
of  the  layer  of  cells  above  described.  A  similar  process 
takes  place  in  the  disarticulation  of  branches  and  of  ripe 
fruits. 

When  disease  or  injury  affects  the  leaves  while  still 
growing — as  in  the  case  of  noxious  vapors  from  chemical 
works  or  kilns,  or  in  the  case  of  insect  injury — its  effects 
are  naturally  most  obvious  and  most  severe  at  the  grow- 
ing points — the  tips  and  margins  of  the  leaf  ;  and  when 
the  margins  become  thus  arrested  in  their  growth,  while 
the  disc  remains  in  full  activity,  the  result  is  a  cup- 
shaped  appearance  or  a  crumpled  surface  resulting  from 
the  dead  or  dying  portions  having  lost  their  elasticity 
and  acting  as  a  curb  on  the  growing  portions.  Sun-burns 
and  especially  the  attacks  of  insects  and  parasitic  fungi 
are  not  so  much  confined  to  the  margins,  at  least  when 
the  leaf  is  not  in  a  growing  state ;  they  produce  their 
effects  in  the  shape  of  circular  or  irregular  spots  of  brown 
decayed  protoplasm.  The  effects  of  frost  and  the  reason 
it  kills  have  been  explained  in  a  former  page.  Nothing, 
however,  can  be  advanced  in  explanation  of  the  reasons 
why  some  plants  of  the  same  species,  like  the  different 
varieties  of  wheat,  are  so  much  more  tender  than  others. 
Death  by  the  leaf  is  rarely  immediately  fatal,  because 


130  PLANT  LIFE   OK  THE  FAKM. 

there  are  many  leaves,  and  they  are  not  often  all 
affected  in  the  same  way  at  the  same  time ;  and,  more- 
over, in  the  case  of  plants  other  than  (t  annuals,"  the 
fall  and  death  of  the  leaves  does  not  involve  the  death  of 
the  plant,  as  before  explained.  Even  in  the  case  of 
annuals,  the  life,  like  the  nutritive  matter,  goes  out  of 
the  leaves  only  to  enter  the  seed. 

Successor  thus  follows  predecessor  in  one  invariable 
rhythm,  and  although  the  limits  of  the  individual  exis- 
tence can  be  but  too  readily  recognized,  the  real '  end  of 
life,  so  far  as  the  whole  race  of  living  creatures — whether 
plant  or  animal — is  concerned,  is  as  incapable  of  being 
appreciated  by  the  physiologist  as  is  its  beginning. 


INDEX. 


ABSORPTION 10 

Amount  of 14 

by  leaves 29,31 

by  roots...   23,  24 

of  gases.. 29,31 

of  water   29 

Alcohol 32 

Ammonia  Salts 17 

Action  of 102 

and  mineral  salts    103 

Annuals : 39 

Anthers...., 84 

BACILLUS 32 

Bacteria 17,26 

Barley 19.  119 

Bast-cells 27,49 

Beet 20,  105,  119 

Branches 39 

Buds 39 

Bud-formation 82 

Bulb* ' 39 

Bundles,  woody 48 

CABBAGE : 113 

Cambium 47,  48 

Carbon 29 

Carbonic  acid 29 

Carnivorous  plants 33 

Caulicle 75 

Cells,  bast 49 

growth  of ...   45 

their  nature 12 

wood .49 

Cereals 20,  87,89,  105 

Changes,  chemical 88 

in  plants 16,  130 

Chlorophyll 12,28,30 

degeneration  of 114,  126 

Circumnutation 52 

Climbing  plants 69 

Clover 15 

Alsike 88 

Color 115 

Colza 79 

Contact,  Action  on  leaves 66 

roots 59 

stems 69 

Cotyledons 74 

Crossbreeding 85,  123 

DEATH,  at  leaf 128 

at  root 127 

from  frost 64 

heat 65 

starvation 127 

Decay 124 

Deoxidation 32 

Diffusion 11 

condition  of 13 

Drainage  water 118 

EMBRYO,  formation  of. 74,  85 

Endogeus , . .  48 

Epidermis 27 

Exogens 48 

Eyes 40 

FALLOW 120 

Farm-yard  manure.- 106,  118 

Feeding  of  plants 9 

Ferments 17,  76 

Fertilization 83 

cross 85,  123 


Fertilization  of  cereals 87 

Fibre  crops 115 

Flowers,  structure  of 83- 

Foliage  crops 113 

Form  of  leaves 26 

as  dependent  on  growth 50 

of  roots 22 

of  stems 38 

Frost,  action  of 64 

Fruits,  ripening  of 80 

GASES,  absorption  of 29 

emission  of 29,  31 

Geotropism 56 

Germination 44,48,  77 

Germs... 17 

Glucose 32,76,77 

Grasses 20,39,91,92 

cereal 20,  87,  105,  123 

pasture •  -  •   94 

Gravitation,  effects  on  roots 56 

effects  on  stems 67 

Growing  points 46 

Growth 44,72 

of  cells 45 

of  leaves 49 

of  roots 47 

of  stems 48 

HAT 19,88 

Heat,  action  on  leaves 64 

onroots 67 

on  stems 69 

(See  also  Temperature). 

Heliotropism 62 

Hops 69,  85 

Hybridization 88 

IMPROVEMENT  of  plants ,121 

Inheritance 73 

Iron 18 

LEAVES 26 

absorption  by 29 

action  in  darkness 31 

of  contact  on 66 

of  gravity  on 62 

of  heat  on 64 

of,  in  light 30 

of  light  on 67 

of  moisture  on 64 

fall  of 129 

feedingby 29 

forms  of 26 

functions  of 37 

growth  of 44 

movements  of 55 

parts  of 27 

sleep  of 63 

Leguminosae 93,96 

Light,  action  on  leaves 62 

roots 57 

stems 68 

Ligule .  27 

Lime,  action  of 18,101 

Liquids,  ascent  of 42 

pressure 43 

MALTING 77 

Mangel 105,  119 

I  Manures 19, 118 

ammonia 102 

I     changeof. 105, 107 

1      disuse  of...  ....106 


(131) 


132 


IKDEX. 


Manures,  effects  of... 20,  73,100,  107,  108 

fann-yafd 106, 118 

mineral    100 

with  ammonia 103 

nitrate 105 

nitrate  of  soda 102 

potash 18 

disuse  of  106 

substitution  of 107 

superphosphate . .  101 

with  ammonia .... 103 

Manuring,  principles  of 19 

Maturation 78,  80 

Meristem 47 

Molecules 10 

Movements 51,  56 

of  leaves 55 

of  protoplasm  . .   51 

of  seedlings 55 

of  stems 53 

of  the  roots 52 

NITRATES 17 

of  soda 102 

Ni  trogen 17 

loss  of 118 

Nucleus 12 

OBJECTS  of  cultivation 119 

Onions 39,  ISO 

Osmosis 10 

Oxygen  in  soil 25 

Inhalation  of 31 

Ovule 84 

PARASITES 33 

Pasture  plants 91 

grown  without  manure. 98 

Perennials 39 

Perisperm 75 

Petals 83 

Petiole 27 

Phosphorus 18 

Pistil 84 

Pith 49 

Plants,  carnivorous 33 

climbing 66 

Plant  food. 16 

Pollen,  action  of 84 

transport  of 84 

Potash  salts 18,10,106 

Potatoes 20,  39,  82,  121,  112, 119 

Protoplasm,  decay  of 125 

its  nature 12 

movement  of 51 

RADICLE . .   53,  60,  75 

Reserve  materials,  transport  of...  .75,  77 

Ripening.    See  Maturation 

Root 22,24 

action  of  contact  on 59 

gravity  on 56 

light  and  heat  on 57 

moisture  on 58 

cap 22 

crops Ill 

fibrils 24 

functions  of 24 

growth  of 47 

hairs 24 

movements  of 52 

nature  and  origin  of 23 

passage  through  soil 60 


Root  stock 38 

Rothamsted,  pasture  at 91 

experiments  18, 19,  21, 35,  78,  109,  121 

Rotation 90, 120 

Runners 38 

SALT 118 

Salts 16 

Sap 41 

Seeds 116 

change  of 123 

Seed  crops 116 

Selection 73 

power  of,  by  roots 20 

Sensitiveness, 56 

Silica 15 

Sodium,  chloride 107,  118 

Stamens 84 

Starch 18,  31,  75,  77 

Starvation 127 

Stem 38 

action  of  contact  on . .  69 

gravity  on 67 

heat  on 69 

light  on 68 

moisture  on 61 

growth  of. 48 

nature  of 38 

uses  of 41 

work  of 38 

Stigma 84 

Stipules 27 

Stomata 27 

Straw 116,  118 

Struggle  for  life 100 

Style.' 84 

Suffocation 27 

Sugar 1 76 

Sulphur ,18 

TEMPERATURE,  effects  of  (See  Heat).. 

Tillering 40,82 

Timber 115 

Transpiration 35 

Transport 75 

Tubers 39,82,112 

Turgescence 45,  51 

Turnips 102,  119 

Twitch 38 

VARIATION 73 

Vegetation,  alternate 121 

gregarious 90 

Vessels 27 

WATER 10 

absorption  of 29 

diffusion  of 11 

importance  of 16 

ingress  of. 11 

supply  of 10 

transpiration 35 

Weeds 93.97 

list  of  pasture 93 

Wheat,  composition  of 15 

embryo 74 

laid 54 

pedigree 74 

produce  of 119 

ripening , 28 

Wood...? 48 

cells 48 

Btructureof 48 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 

OVERDBlflffi>I<n>4!r<B'  I  n 


MAR  21  1939 


LD  21-95m-7,'37 


U.C.  BERKELEY  LIBRARIES 


5266 


BIOLOGY 

LIBRARY 

G 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


